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Old January 16, 2019, 17:43   #1
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Gas port size for an AR in 5.45x39?

The gas port on my new McGowen 18 inch barrel is .082 and the rifle does not cycle far enough to the rear to eject the spent cartridge. It cycles partially but then rechambers the spent case jamming it back into the chamber requiring pogoing the action to remove the spent case.
On a FAL I would just increase the gas by closing the adjuster a few clicks until it cycled reliably. On an AR the only way to adjust the gas is by drilling out the gas port on the barrel. If you open it too much there is no going back so I am looking to find out how much to open the port from .082 to the ideal. It may take a few attempts but that is ok as long as I donít go too far.
Any suggestions?
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Old January 16, 2019, 18:54   #2
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There are a lot of variables here, what is the gas system length, rifle? What weight buffer, what recoil spring? Could it be over gassed and unlocking too early? If you insist it is the gas port, yes there is going back if you drill the port too large. There are a ton of adjustable gas blocks on the market.
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Old January 16, 2019, 19:08   #3
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Thanks.
18 inch barrel, rifle length gas tube. Gas tube is a Rock River National Match.
Judging by what I have experienced with FALs I am not getting enough gas to the bolt/carrier assembly.
I did change out the lower with one from another functional 5.45x39 lower with a captured recoil spring, still the same, failure to cycle fully.
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The fear of God is the beginning of wisdom.

Matthew 25:1 thru 25:10 Be ready!

The written word sometimes like poetry is never really finished but merely abandoned.

I live alone in the middle of nowhere with two dogs and a cat, what do you think about that.

The wind blows, the rain falls, the flag snaps its bravery in the dark as two dogs boil for attention at my feet.

Of course it is a true story. You just couldn't make up something like that, no way.
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Old January 16, 2019, 20:12   #4
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Did you install the gas block? Is it alinged properly?
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Old January 16, 2019, 20:17   #5
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I'm thinking port should be around .093 on rifle length?
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Old January 16, 2019, 20:32   #6
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Yes, I did install the front sight gas block and it is aligned to the best of my ability, which is considerable. LOL!
Just joking.
I did take special care to align the sight correctly. Rear sight centered and front sight set to horizontal point of aim, front and rear are aligned. The front sight is the standard AR rifle sight but has set screws for rotational alignment.
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The fear of God is the beginning of wisdom.

Matthew 25:1 thru 25:10 Be ready!

The written word sometimes like poetry is never really finished but merely abandoned.

I live alone in the middle of nowhere with two dogs and a cat, what do you think about that.

The wind blows, the rain falls, the flag snaps its bravery in the dark as two dogs boil for attention at my feet.

Of course it is a true story. You just couldn't make up something like that, no way.

Last edited by Sagerider; January 16, 2019 at 21:02.
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Old January 17, 2019, 05:45   #7
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I don't have one in 5.45x39, but I have .308 rifle length gas, port at .093 and if I'm not mistaken 5.56 was the same.
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Old January 17, 2019, 05:47   #8
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Mid length is usually around that .081 or so I believe.
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Old January 17, 2019, 08:30   #9
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there is also the issue of bolt carrier mass.

On the 5.45 AK, the the bolt carrier has several lightening cuts compared to its 7.62 cousin (Bulgy, left side, Romy hollowed out)

I wonder if you could drill and tap the barrel for a SCAR 16 gas port orifice. Then just drill out until you're happy and if you go oversize, just unscrew and replace.
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Old January 17, 2019, 11:06   #10
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There are adjustable gas blocks available but if your gas port is too small that won't help.
I just put a superlative arms adjustable gas block on a new White Oak Armament 18" barrel. I waited for the barrel to be delivered before ordering the set screw type gas block as I had to be sure there was a dimple on the barrel for correct alignment. There was thank goodness as I've not had real good luck aligning clamp on type gas blocks very well.
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Old January 17, 2019, 11:34   #11
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Quote:
Originally Posted by davedude View Post
I've not had real good luck aligning clamp on type gas blocks very well.
I forget who did it, but someone makes barrels with a keyway at the journal shoulder and a corresponding key in the gas block. Or the other way around. But it makes lineup brilliant.
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Old January 17, 2019, 12:05   #12
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If you've pulled the gas block have you inspected the block where it alligns with the gas port? Should see the carbon blackening where the 2 meet, and if there is a leak and the gas not fully entering the tube. Misaligned gas ports will cause it. Also verify you don't have a gas leak around the where the gas tube enters the block.

Next, the other end, ensure your gas key is properly tightened and staked, and while there pull the bolt and verify your gas rings are in good shape.

Someone mentioned overgassing. If that is the case you'll see damage to the case rim, the extractor, or both. Unlikely with a rifle-length system but anything is possible. Simple and cheap improvement though is the o-ring addition to the extractor if you don't already have one. This increases extractor pressure if the spring is weak.

Next is system mass. If you're running a heavier buffer lighten it or get a lighter one. As mark mentioned a lighter carrier may be necessary. If you're running an M-16 carrier these are the heaviest and have the most mass, look for an "AR-15 carrier that has less material to the rear.

You can run a lighter recoil spring and this may help as well.

Lastly is friction is the system. If you have a non-standard cam pin they sometimes have clearance issues with the upper receiver and will show contact wear in the top of the upper. If that's the case simply remove a little material from the path of the pin. Might check the inside of the buffer tube as well for any obstructions.

Somewhere above is your problem though. You've either got too little gas, too much mass, or something affecting the action. More than 1 problem is also possible, but eliminate all of the above and I bet you'll be good.
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Old January 17, 2019, 18:18   #13
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You could lighten the reciprocating mass as has been suggested. There are a shit load of lightened carriers, buffer weights, captured spring systems generally for 3gun for a flatter shooting rifle, fast split times etc. If you have ruled out other errors, opening the port won't cost much more than a drill bit.
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Old January 17, 2019, 20:55   #14
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Get a good adjustable gas block and over drilling is not really an issue unless get totally silly with bit size. While I dislike lightweight carriers this is one situation where it may be a requirement. If already have a carrier and don't want to buy another can slowly lighten it a little at a time on your mill and not invest anything more than time rather than money. I would open the port to 0.093/0.095" install a Superlative Arms Adjustable gas block and carry a couple lightweight buffers in my pocket when take it to the range and see if can dial it in without major modifications. Have been liking the Superlative Clamp-On blocks as easy to tweak if not perfectly aligned.
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Old January 17, 2019, 22:43   #15
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My intent for this rifle is a truncated full length down to 18 inches with standard iron sights. This configuration reduces the barrel from 20 to 18 which reduces the time the gas has to enter the port and activate the bolt mechanism. Granted not by much but the bullet and pressure leaves the barrel earlier none the less.
Adjustable gas blocks I have seen do not have the traditional front sight tower. I like iron sights and even with my fading visual acuity I can do pretty well at 130 yards and less. I like the shorter barrel because for me it feels better in my hands and balances better while using the carry handle.
I removed the front sight and everything looks to be lined up correctly by the carbon stain and the front sight gas passage is large enough for any slight misalignment. As I stated before I swapped lowers with one of the same caliber that works very well with a 16 carbine barrel. No love with the swapped lower so my conclusion is the problem is in the new upper.
I will change out the bolt assembly with one I know works and go from there. The next step will be to open the gas port hole in the barrel incrementally until I have full function.
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The written word sometimes like poetry is never really finished but merely abandoned.

I live alone in the middle of nowhere with two dogs and a cat, what do you think about that.

The wind blows, the rain falls, the flag snaps its bravery in the dark as two dogs boil for attention at my feet.

Of course it is a true story. You just couldn't make up something like that, no way.
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Old January 18, 2019, 05:29   #16
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https://www.jprifles.com/buy.php?item=JPGS-2FS

Just in case, but I doubt you'll need it.
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Old January 18, 2019, 20:51   #17
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I put a 15" ALG V3 railed handguard on my 18" rifle gas barrel. The SA adj gas block hides underneath but if I want I can put a flip up front sight out on the end and get a little bit more distance between front and back irons than a front sight gas/tower would allow.
Not that it would help me much.
Hats off to you for being able to use irons. I have to use glass and it's going to cost me.
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Old January 19, 2019, 01:27   #18
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Thanks emcroy! Never knew anyone made them.

I do need to wear glasses when shooting with iron sights but reading glasses with just enough power to get a more focused front sight. If you haven’t tried using reading glasses you should try them. There are also guys making rear iron sights with a small magnifier built in and ok for service rifle matches I have been told. The one I have works very well to get a crisper front sight with old eyes.
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The fear of God is the beginning of wisdom.

Matthew 25:1 thru 25:10 Be ready!

The written word sometimes like poetry is never really finished but merely abandoned.

I live alone in the middle of nowhere with two dogs and a cat, what do you think about that.

The wind blows, the rain falls, the flag snaps its bravery in the dark as two dogs boil for attention at my feet.

Of course it is a true story. You just couldn't make up something like that, no way.
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Old January 19, 2019, 14:00   #19
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I posted a thread on how to convert a standard front sight tower to adjustable gas with a thirty cent screw (hardened to resist erosion) along with a drill press and tap set. If can't find it will repost the pictures as very easy and saves major dollars over a JP unless want to spend the money. If budget is not an issue then the JP is easy peasy. I have a jig now that holds a complete upper receiver all squared in my mill so can mill and tap the front sight block without removing muzzle device and front sight tower to do the conversion.
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Old January 19, 2019, 17:27   #20
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Speaking of lightened reciprocating mass. I have .308 that I'm running, criterion barrel 16" rifle gas length, port is .093. I'm running a full weight carrier and H3 5.4 ounce buffer, full mass bolt carrier group is around 18 ounces. Gas block is wide open to get lock back on empty mag. I'm planning to eventually run a titanuim carrier and light buffer and reduce the gas a bit. I think it's a win win. Lighter weight overall and less heavy shit slamming back and forth, optic will appreciate it I'm sure.
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Old January 20, 2019, 18:23   #21
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Sooo, I opened up the gas port bit by bit until I got to .093. Some improvement but no joy, case still stuck in the chamber. I did place an O ring under the extractor to eliminate that issue. I changed out the lower again with a reduced recoil spring, captured type, that works perfectly with another barrel of the same caliber. Next I exchanged the bolt carrier with a lighter unit, not full rear shroud type. Better, no stuck cases and full ejection but not fully rearward to lock open on an empty magazine. It catches on the bolt carrier instead of the bolt like it should.
Looks like I am making progress.

So buffer and recoil spring is the next step.
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The fear of God is the beginning of wisdom.

Matthew 25:1 thru 25:10 Be ready!

The written word sometimes like poetry is never really finished but merely abandoned.

I live alone in the middle of nowhere with two dogs and a cat, what do you think about that.

The wind blows, the rain falls, the flag snaps its bravery in the dark as two dogs boil for attention at my feet.

Of course it is a true story. You just couldn't make up something like that, no way.
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Old January 21, 2019, 18:40   #22
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Have found Tubbs chrome silicon flatwire buffer springs work in 5.7◊28 to 338 Federal and every cartridge in between. Any AR 15 or AR 10 build that is going to be classified as a fighting rifle that may be taken from the pile in a life or death situation gets a Tubbs Flatwire Buffer Spring. Have had them fix rifles that had issues but never had them be the cause of an issue if used from onset of build process. Currently using them in 5.7◊28, 223/5.56, 6.8 spc II, 458 SOCOM, 6XC, 308/7.62◊51 and 338 Federal. Have used them in 20 Tactical/TAC 20, 204 Ruger, 300 BO and a few wildcats. YMMV and all other Internet disclaimers.

What BHO are you using? Assume you have checked the BHO for binding and excessive pressure. I prefer DPMS milspec and often massage them by shaving so they interact with all moving parts properly. Shaving a small amount off top along with polishing can help with overall operation of rifle. Properly fitted the BHO does not exert excessive pressure on the bolt as it travels and has just the proper amount of meat to engage and lock. Have seen builds breaking BHO's in LGS with owners scratching head. A little examination of wear on disconnect and bottom of bolt can give clues and also seen people mix up the bolt catch spring with a disconnect spring causing issues. Sometimes the detent hole is not machined deep enough and a coil or two of the spring needed clipped for the detent to travel correct depth.

Odds are your still short stroking a tad and need to get that resolved. Buffer and buffer spring swap will either make it better or worse. If worse then still not getting enough gas. I might go for opening gas port to 0.096" before spend more money on parts unless have them in your build kit already. Not too much of a difference but may be enough to make all work. Before opening port past 0.096" would go through everything in the system two or three more times. I did find a thread on a machining site I have found useful over the years but also seen people recommend stuff which would not do to someone I disliked rifles. Thread they had on 5.45◊39 recommended a 0.125" port for a 20" rifle length 5.45◊39 and a 0.095" port for 16" carbine length gas but no port sizes for 18" tubes. Most of the posters are mix of professional and basement machinists and some seem more professional than others. Seems they like big ports in their 5.45 builds though. If go too big an adjustable gas block is an easy fix.

Found this about similar situation:
Quote:
Ordered a McGowen 20" stainless barrel in 5.45x39 with a rifle length gas system. I am running this on an A2 lower with mill spec Tigger/ wolf extra power hammer spring and standard mil spec rifle buffer/spring. The bolt is ballistic advantage on a semi auto carrier. The barrel came with a 0.082" diameter hole. This didn't even eject the spent cases. I've stepped up in size 0.086", 0.089. 0.0935, & currently it's at 0.09375 (3/32). It will eject spent cases and lock the trigger back but will not load the next round. It's throwing cases about 5' away at the 3 o clock position. This is with both surplus 7n6 and commercial ammo.*Should I continue stepping the the gas port diameter or is there something else I should try and change first?*
Just spent 20 minutes reading links to issues with 5.45◊39 AR 15's. Seems most people who solved them easily did so by opening gas, swapping to lighter buffer or combination of both. I would get an easy to adjust on the fly gas block like a MicroMOA Govnah, Noveske Switchblock or other where have normal setting, suppressed setting and "emergency full gas" setting can change easily on the fly. Only point I see to the 5.45◊39 is using inexpensive surplus ammo. This means corrosive primed, fully corrosive nasty ammo, steel case, mix of crap ammo that makes Wolf look good so building the rifle to run no matter what would be prime issue. Would most likely open up that port, pull one of my undrilled MicroMOA Govnah gas blocks then drill one of the three holes same size of gas port for full gas emergency mode, other that runs properly with most surplus ammo and third to run with good commercial ammo.

Found this article. Guy loves his 5.45◊39 but warns about buying reputable parts. I agree with his opinion on corossive ammo. Used to shoot a lot and have a half metric ton of corrosive stockpiled. If you see me cleaning an AR, AK, etc it means it probably saw some corrosive ammo. Otherwise run them till they needed cleaning a long time ago unless it's going into storage.

https://www.alloutdoor.com/2014/05/2...5-45x39-ar-15/
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Old January 22, 2019, 17:39   #23
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This has been an interesting read. I wanted an AR in the caliber before one was ever built, nothing was available at the time. Then I believe it was Anderson Arms? that came out with .22 Gengis. Or was it Phoenix?
Which ever....

I looked into obtaining this upper (only available as an upper at the time) but then mags became an issue, wasn't sure what would work.

Gave up and got into the AK74 for my needs at the time.
Later when I revisited the thought of an AR in 5.45 some more thoughts came to me. 1) What are the possibilities of grabbing the wrong rifle/mag/caliber combination in a quick grab on the way out the door? And 2) why bother when surplus ammo is history?

The thought of a lightweight flat, fast shooter with a good muzzle brake and zero muzzle climb that would give .223 the middle finger was a dream I never realized. Instead, I used a slightly modified AK74 that was damn near the realization of that idea but without the aftermarket accs the AR enjoys. And give the AR world the middle finger, it did.

Today I still want another 74, Have even entertained the idea of liquidating or trading. But the lack of cheap surplus still dampens the love of the idea, most of what made me like the caliber in the first place.

Good luck to the OP with his project. You'll get it.
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Old January 22, 2019, 21:56   #24
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I ordered a 3 ounce recoil buffer, about 4 or 5 ounces less than standard so that is on the way. I took a standard rifle buffer apart and removed the weights that I understand are designed to be used in full auto rifles and carbines to prevent bolt bounce, the bolt bouncing back after chambering a round. This condition is specific to full auto not semi auto. Looking at the Tubbs flat wound springs too., thanks for that tip.

To answer the potential problem with similar rifles in 2 or 3 different cartridges I paint them accordingly and the same for the magazines. Brown goes with brown, green goes with green and black goes with black, of course you can paint them any color you wish. I only paint the plastic bits on the rifle like the forearm or both the forearm and stock. The magazines get paint on the bottom third only.

I forgot to call Rock River and ask if there is any difference between a standard gas tube and their National Match gas tube which I have mounted. They sell either type with the standard tube is 2 bucks more so there most likely is a difference, both should be stainless steel. I will call tomorrow.

So tomorrow I will give the “no weights installed” buffer a go and see what that does. Reducing the recoil spring strength by using a captured spring device is always an option but. I am concerned of a weaker spring not having enough power to reliably strip a round out of a full magazine when the bolt hold back lever gets smacked to release the bolt. Again drilling out the gas port more than the .093 it has already been drilled to, maybe .98? I am reluctant to go more because of the small diameter bore.

In my humble opinion the AR with iron peep sights is easier for me to produce tight groups consistently because of the generally better sights over an AK and also the increased sight radius. I can also lock into the AR rifle better and more consistently making it a much more precise tool.

I will post up after I test the no weight buffer tomorrow.
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The fear of God is the beginning of wisdom.

Matthew 25:1 thru 25:10 Be ready!

The written word sometimes like poetry is never really finished but merely abandoned.

I live alone in the middle of nowhere with two dogs and a cat, what do you think about that.

The wind blows, the rain falls, the flag snaps its bravery in the dark as two dogs boil for attention at my feet.

Of course it is a true story. You just couldn't make up something like that, no way.

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Old January 23, 2019, 17:11   #25
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No weight buffer was of no help. Single round test, bolt locks on bolt body not the bolt itself as it should. So the only choice is either a softer recoil spring or a larger diameter gas port. The lighter bolt did help but I would like to avoid a princes rifle with limited reliability issues and requires special parts.

I did called Rock River today and was told the only difference between the standard gas tube and the National Match tube is the bend making room for the National Match hand guards. So no love there either.

I think the problem in a nut shell is the short dwell time that full pressure is applied to the bolt. I have had no issues with my 18 barrel with 5.56x45 NATO or .223 ammo.

My impression at this point is go with a 16 or 20 inch length barrel for the 5.45x39 on an AR rifle. This is just my suggestion unless you like pain.
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The fear of God is the beginning of wisdom.

Matthew 25:1 thru 25:10 Be ready!

The written word sometimes like poetry is never really finished but merely abandoned.

I live alone in the middle of nowhere with two dogs and a cat, what do you think about that.

The wind blows, the rain falls, the flag snaps its bravery in the dark as two dogs boil for attention at my feet.

Of course it is a true story. You just couldn't make up something like that, no way.
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Old January 23, 2019, 18:36   #26
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Frustration mounting.
So I opened up the gas port to .101 from .093. Which locked the bolt fully rearward, yea! But wait there is more! The spent case is not being extracted, great. Swapping parts from one rifle to another I found the bolt and carrier from the functional rifle works perfectly in the 18 barrel unit. Full lock back and extraction. Looks like I have a problem with the bolt in the non functional assembly. The round will not fully chamber in the 16 inch barreled unit using the non functional bolt. I tried the bad bolt just to see if it would function which it does not. I will take the O ring out and see how that goes next.
Bottom line is I have full function in both rifles but only with one bolt assembly.
Weird!

O ring removal made no difference. Bad bolt/extractor but nothing that is obvious.
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The fear of God is the beginning of wisdom.

Matthew 25:1 thru 25:10 Be ready!

The written word sometimes like poetry is never really finished but merely abandoned.

I live alone in the middle of nowhere with two dogs and a cat, what do you think about that.

The wind blows, the rain falls, the flag snaps its bravery in the dark as two dogs boil for attention at my feet.

Of course it is a true story. You just couldn't make up something like that, no way.

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Old January 24, 2019, 20:52   #27
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Well damn! Never thought about bolt/ carrier being the problem. It's not one of those "porris" bolts is it?
Thanks for posting, been interesting. If you've a mind to please follow up with what you find wrong with that bolt.
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Old January 24, 2019, 21:26   #28
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It is the extractor!
Placing a cartridge into the bolt, removed from the carrier and no firing pin, the extractor will not allow the cartridge to align with the bolt when the cartridge was pushed into place. Problem is the inside portion of the lip on the extractor is slightly too thick. What was happening was when the cartridge was chambered the extractor was not snapping over the case rim. The bolt would lock up ok but the extractor was not over the case rim, no extraction resulted. Testing both the bad one against the good one this defect shows up.
What I will do is take a pointed diamond rotary tool to the inside lip of the bad extractor to remove a small amount of material. I checked the bad extractor against a 5.56x45 extractor and they are not the same so a mistake of using the wrong extractor was not the problem. A little careful tweaking to the inside lip of the extractor should cure the problem.
As Gunplumber stated earlier I had more than one problem with this rifle. #1 the gas port was too small and #2 the extractor was not going over the case rim when in battery.
Note: Opening the gas port to .101 diameter solved the gas issue in this rifle and may not be the cure for yours. Keep in mind this is an 18 barrel with a standard rifle chamber to gas port length. This results in a very short time the gas has to operate the bolt carrier and bolt before the bullet exits the muzzle. Increasing the gas flow solved this issue.
Note: This was all done using standard 7N Russian surplus ammo.
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The written word sometimes like poetry is never really finished but merely abandoned.

I live alone in the middle of nowhere with two dogs and a cat, what do you think about that.

The wind blows, the rain falls, the flag snaps its bravery in the dark as two dogs boil for attention at my feet.

Of course it is a true story. You just couldn't make up something like that, no way.

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Old January 24, 2019, 23:20   #29
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While it's somewhat of an apples and oranges sort of thing, I thought that I'd mention that the S&W M&P-15R (full factory gun) that I have has been 100% with Wolf 60gr ammo, both FMJ and HP.

Of course, it has a carbine length gas system with a 16" M4 profile barrel, and I don't feel inclined to pull off the front sight tower to check gas port size. Then again, knowing the gas port size of this carbine wouldn't probably help much here anyway. It has an increased power hammer spring (factory) for the harder primers on 7N6 ammo. It has a standard carbine buffer spring, a standard carbine buffer (81gm) and an AR-15 (not M16) bolt carrier...

Given new info about the extractor problem on your rifle, I should point out that your original extraction/rechambering problem could have occurred even with the correct gas port size. I'm assuming that you tried with rounds in the mag below the chambered round...

Also, gas blocks can be funny things, especially since some are designed for use with front handguard retainers on the barrel and some (usually for free-floated, railed handguards) are designed to fit tightly against the barrel seat. While the difference is small, so is the gas port hole and I have seen a few problems from the 'mismatch.'

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Old January 25, 2019, 05:58   #30
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If you look back in this post you will see that the bolt would not lock to the rear fully. When it did start to lock back it was on the carrier not the bolt as it should be. The last time I opened the hole to .101 was the first time it locked back fully with the bolt catch in front of the bolt. I am thinking the 7N Russian does not produce the barrel pressure that the 5.56x45 does so having to send more gas to the carrier is not a surprise in this case.
With the 16 inch barrel the time the bullet is between the gas port and the muzzle is considerably longer compared with the 18 inch rifle. Some refer to this time as dwell time and is most likely the proper terminology. The pressure is also higher the closer it bleeds off from the chamber. This whole thing makes perfect sense to me now that things are working as they should gas wise. Just for a little more information the spent case goes about 6 to 7 feet to the rear at around the 5 o’clock position possibly indicating a slight over gas condition but I am not worried about it.
The extractor back edge is flush with the bolt face so the pin hole for it is correct. It will only require a small amount of material to be removed on the under side of the hook. Too much material in this spot did not allow the extractor to snap over the case rim so no extraction which had little or nothing to do with the gas issue, it just added one more problem. A note of interest is that I also checked the ejector making sure it would recess correctly down flush with or below the bolt face when depressed which it does.
My fully functional and accurate AR in 5.45x39 is a 16 inch barreled carbine and functioned perfectly from day one. After a bad barrel was swapped out accuracy improved greatly. Exactly why this barrel is not up to snuff I have no idea and this bad barrel now rests in some obscure corner in the office/gun room unloved.
As for accuracy with this new 18 barrel I have no clue yet after getting all my atttention to get the rifle to function properly. Dialing it in will come after surgery on the extractor scheduled for later this afternoon.
This all was frustrating to some degree as information on port size is hard to come by. I called McGowen twice reguarding this issue but the gunsmith with the answers had some personal issues with a new baby coming home and never called me back. In a way I am glad because it made me figure this out for myself. I fully expect this 18 barreled rifle to fully function once I trim the extractor.
You might wonder how well does it shoot and so do I. I hope it shoots as well as the 16 inch barreled rifle.
I will post up after the extractor trim, stay tuned.
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The fear of God is the beginning of wisdom.

Matthew 25:1 thru 25:10 Be ready!

The written word sometimes like poetry is never really finished but merely abandoned.

I live alone in the middle of nowhere with two dogs and a cat, what do you think about that.

The wind blows, the rain falls, the flag snaps its bravery in the dark as two dogs boil for attention at my feet.

Of course it is a true story. You just couldn't make up something like that, no way.

Last edited by Sagerider; January 25, 2019 at 06:21.
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Old January 25, 2019, 13:10   #31
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Quote:
Originally Posted by Sagerider View Post
If you look back in this post you will see that the bolt would not lock to the rear fully. When it did start to lock back it was on the carrier not the bolt as it should be. The last time I opened the hole to .101 was the first time it locked back fully with the bolt catch in front of the bolt. I am thinking the 7N Russian does not produce the barrel pressure that the 5.56x45 does so having to send more gas to the carrier is not a surprise in this case.
With the 16 inch barrel the time the bullet is between the gas port and the muzzle is considerably longer compared with the 18 inch rifle. Some refer to this time as dwell time and is most likely the proper terminology. The pressure is also higher the closer it bleeds off from the chamber. This whole thing makes perfect sense to me now that things are working as they should gas wise. Just for a little more information the spent case goes about 6 to 7 feet to the rear at around the 5 o’clock position possibly indicating a slight over gas condition but I am not worried about it.
The extractor back edge is flush with the bolt face so the pin hole for it is correct. It will only require a small amount of material to be removed on the under side of the hook. Too much material in this spot did not allow the extractor to snap over the case rim so no extraction which had little or nothing to do with the gas issue, it just added one more problem. A note of interest is that I also checked the ejector making sure it would recess correctly down flush with or below the bolt face when depressed which it does.
My fully functional and accurate AR in 5.45x39 is a 16 inch barreled carbine and functioned perfectly from day one. After a bad barrel was swapped out accuracy improved greatly. Exactly why this barrel is not up to snuff I have no idea and this bad barrel now rests in some obscure corner in the office/gun room unloved.
As for accuracy with this new 18 barrel I have no clue yet after getting all my atttention to get the rifle to function properly. Dialing it in will come after surgery on the extractor scheduled for later this afternoon.
This all was frustrating to some degree as information on port size is hard to come by. I called McGowen twice reguarding this issue but the gunsmith with the answers had some personal issues with a new baby coming home and never called me back. In a way I am glad because it made me figure this out for myself. I fully expect this 18 barreled rifle to fully function once I trim the extractor.
You might wonder how well does it shoot and so do I. I hope it shoots as well as the 16 inch barreled rifle.
I will post up after the extractor trim, stay tuned.
After reading this comment, I see that I didn't do a good job of what I was trying to say. I certainly was not trying to say that I thought that you were wrong about the gas port being too small initially...

My poorly expressed point was mostly that, since everything in a machine like a semi-auto rifle is designed to work as a unit, parts not performing correctly can lead to interesting failures in the entire machine. For example, the extractor not gripping the case 'rim' and holding it against the bolt face could have somewhat unexpected system failure consequences, which often makes the attempt to isolate the actual problem so 'interesting'...

I have seen a number of cases where ARs were so overgassed that they would rechamber the fired case while not locking open with no cartridges in an empty mag below and, even with cartridges in a magazine below, rechambering the fired case and not leading to the expected jam from trying to chamber the next cartridge with the old one still there. Presumably, the bolt velocity was so high that the bolt catch can't catch the bolt (in the first case) and the spring isn't pushing up cartridges fast enough to have the returning bolt catch them (in the second case). Fired cases rechambered in this manner are really fun to remove since the returning bolt velocity rechambers them with great force (oh, wait, you probably know this since rechambering even with low velocity is fun to deal with... ).

My point is that I understand your frustration in isolating the problem(s). For example (and digressing for a moment), when Wolf came out with the Taiwanese T91 uppers, I quickly picked one up. It's an inspired design. If the completed units came directly from Taiwan, I'd have several. Unfortunately, they don't and the American connection has resulted in my having only two (and I had to work hard to get them 'right'). The first one that I received had cycling problems (first assessment, not enough gas). Firing 55gr Wolf Gold .223 Rem. (really M193), the rifle would eject the case, dribbling them out at my feet, but would fail to pick up the next round (due to low gas). Since I had previously fired the ammo in ARs and had checked velocity with US M193, I guessed that the ammo wasn't the problem.

So I took the rifle into the shop, removed the handguard (which was really jammed on (and which should have told me something then since they are really easy to take off it turns out, but hindsight is always so much clearer)), and checked the gas port. Without checking my notes, I think that the port was 0.071-0.073" (which sounded about right). I chased the hole with a drill (not increasing the size), thinking that some small obstruction or burr might be limiting gas flow). Firing again, no joy..

So, thinking that opening the port a couple of thousandths wouldn't hurt anything, I took a pneumatic drill and, while steadying the drill against the gas block (and applying fair pressure against it), I was just ready to 'ream' the gas port when the gas block (which has the front sight on the T91) shifted dramatically. It turns out the the gas block journal on the American profiled and finished barrel was dramatically undersized, allowing the gas block to flop around just like a dying chicken (it's pinned to the barrel on the top). I have a nice 15 second video of flopping the gas block around on the barrel, made just in case I ever needed it).

Well, that solved the functioning problem. The gas port was just fine. Of course, to work, that assumes that the gas block is tight on the barrel...

I sent the upper back to Wolf for barrel replacement, which they did and returned the unit quickly. I fired 30rds though it on return to check functioning and sight it in with the Vortex Strikefire II. All worked well...

Then again, after many months of fixing problems with the second T91 from Wolf, with a couple of replacements from them, and finally ending up with a unit that worked (with an M16 bolt, not with the one that came with the rifle, which involves another story too long for here), I finally checked the headspace of the first upper (that functioned with the Wolf Gold (and other) ammo just fine). No close on the GO gauge... Well, at least I can fix that problem easily...

Sorry for the digression. My point is mostly that I understand (and sympathize with) your frustration on solving your functioning problem...

By the way, you mention 7N ammo a couple of times. Are you using both 7N6 and 7N22, or something even else...

I'm happy that your problem seems to be resolved...

Forrest
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Old January 25, 2019, 16:16   #32
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The fun in all this is working with your mind to figure out a problem, which I very much enjoy. Problems can be frustrating but that makes them interesting.
Glad you got yours running correctly.
This is my first adventure with gas port size on an AR rifle and with a different cartridge than a .223/5.65x45 so this added to the mix. The ammo I am using is the 7N6 standard Russian military surplus that used to sell for $150.00 a can but has since gone to $250.00 if you can find it.
The velocity is reported to be around 2,800 FPS which is down considerably from the 5.56x45 of around 3,100 to 3,200 FPS and with that I assume the pressure is lower as well. As we all know assumptions can really kick you in the nuts sometimes.
A South Carolina friend of mine once demonstrated his Southern wisdom at a business meeting in such a way that I will never forget. This is what he said.
“When I am driving my car down the road I just assume that the wheels are turning, I don’t have to stick my head out the window to check.”
Likewise when dealing with this problem of correct gas for proper function I am making the assumption that a cartridge with less velocity, with roughly the same bullet diameter and weight translates to lower pressure. Of course I could be wrong but this is how it looks to be. Without doing the math yet I suspect that the amount of gas increase you get when increasing the hole diameter is not a straight line. Going from .093 to .101 is a .008 increase, a big step but going from .082 to .093, an .011 increase with no apparent improvement tells me something interesting.
The area of a circle = pi x the radious squared. As the hole diameter increases the area increases but it increases faster the larger the hole diameter. I could have been better off with going from .093 to say .096 or .097 instead of jumping to .101, just something to think about. I went from .082 to .093 with no improvement, failure to lock the bolt back on an empty magazine. Then from .093 to .101 that gave me what appears to be too much gas but it does lock the bolt fully on the bolt hold open where as before it was locking on the carrier not the bolt at .093.
By going back from the AR15 carrier to the heavier M16 carrier I might be just fine. We will see how that works out.
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Matthew 25:1 thru 25:10 Be ready!

The written word sometimes like poetry is never really finished but merely abandoned.

I live alone in the middle of nowhere with two dogs and a cat, what do you think about that.

The wind blows, the rain falls, the flag snaps its bravery in the dark as two dogs boil for attention at my feet.

Of course it is a true story. You just couldn't make up something like that, no way.
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Old January 25, 2019, 17:32   #33
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I have built very few new poodle shooters in past three months due to chasing issues on others home brew nightmares. Most are simple, others are not but after taking in at least 100 randomly slapped together kithen table builds in myriad of cartridges most times know what it needs while still in shipping or repair rack at LGS. Sometimes only fix is a total disassembly and reassemble going through all the proper steps. Have had several rifles that were almost non functional with buffer swaps and other easy attempts by builder that when it arrived at LGS and gave a good inspection tore it down to every pin and spring, squared front of receiver, screwed back together using proper torque values, correct BHO & disconnect springs (how do you mix those up?) in correct locations and rifle ran flawlessly with everything but Wolf. Contact owner and If said they use cheapest steel case ammo can find open the port on a 5.56 to 0.080" unless already that big or bigger then either open it one size up in macnist bit set or swap buffer.

Admitting I am a barrel wore and tend to buy better tube than most builders other than a buffer swap at range no matter cartridge have only had to open one name brand barrel port to make the rifle work. Usually reducing flow with an adjustable gas block as select buffers. I almost always use full weight/full auto M16 bolt carriers but never built a 5.45 or even worked on one. I dislike lightweight bolt carriers and have run full auto M16 carriers in 20 Tactical/TAC 20, 204 Ruger, 223/5.56/Wylde, various 6mm's, 6.5 Grendel, 6.8 spc II, 270 AR, 300 BO and more. Referring to post above about mixing up magazines for a Kaboom at one time I had poodle shooters in eleven cartridges counting wildcats.

Gun Plumbers comments were responsible for me thinning the herd and sold a pile of love round count barrels off. Due to 300 BO in 5.56 KaBooms happening several times a week at one very popular local range I sold off both my 300 BO barrels. Then all four of my 20 calibers went followed by my 6.5 Grendel. Sold a pair of 6mm wildcats and my 270 AR. Except for wife's pair of 5.7◊28's with bump triggers I thinned herd down to only 223/5.56/Wylde and 6.8 spc II for a while. This is when I suddenly found myself with a dozen the eighteen and now over twenty 6.8's. Added quite a few 223/5.56/Wylde in odd lengths and twist rates then came the 22 Nosler. Four Nosler's later realized still didn't have really good subsonic rifle as 6.8 even with a Bison fast twist barrel and their 200 grain projectiles are not great subsonic rifles. Thus entered the 458 SOCOM into the fleet of which have four now.

Have very meticulous method to keep any mistakes mixing up magazines but with 223/5.56, 22 Nosler, 6.8 spc II and 458 SOCOM cannot find a combination where any will chamber and fire in the wrong rifle such as 300 BO in a 5.56. Loaded a half dozen dummy rounds in all mentioned cartridges using new primers after removing the anvils and soaking them in machining fluid for a few days then scarping out as much priming compound as possible. Loaded the dead primers in vented cases (four holes drilled in case walls), seated a bullet then began sticking wrong round in wrong rifle on purpose. Tried multiple rifles in each cartridge with dummies. Never got a single dented primer. Seldom got rifle in battery except using 5.56 in 22 Nosler but the round fell so deep firing pin didn't dent primer and feel if it did on a live round rifle would not KaBoom though may ruin the throat of a nice barrel.

Being ADD and OCD plus retarded get bored easily. I have bought a few wildcat barrels to play with but they have a special place in reAR of a vault they live when not going to the range. Will not get mixed up because leaned in corner and grabbed wron magazine. Their ammo is kept in a locker except when take one to range. Have built, shot and sold a few wildcats in the process. Being an experimenter and enjoy working up loads the occasional experiment keeps me from getting bored. Have almost fell victim to introducing the TAC Six into my fleet. It's based on a 6.8 spc II case necked down to 6mm. Only issue is a mixup of jamming a 6.8 mag in one would be catstrophic. It's not that super of a round to replace my fleet of 6.8's so for now have one that lives in the wildcat vault except when want to surprise someone on a 50 yard to 600 yard course. The TAC Six is a flat shooter and has longest point blank range of any poodle shooter currently own.

If had a big pile of 5.45◊39 ammo stockpiled from when it was dirt cheap Missing that oportunity was dumb. Rather than build an AR to shoot it would run it through a proper combloc rifle. Have more 7.62◊39 than could easily count and never been tempted to build an AR to shoot any of it. Have AK's, SKS's and SKS-M's if ever need to lob any. Only 7.62◊39 we do shoot (mostly the wife) is 160 grain cast gas check reloads from our semi customized SKS's. I prefer an SKS with twenty round box mag and bag of stripper clips to an AK for plinking. As expensive as 5.45 has become doubt will jump into it now. Should have a couple of full pallets but was dumb and missed out while it was cheap. Good luck to the OP.
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Old January 25, 2019, 18:08   #34
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I'm not sure what bolt you are using, but when I built my 5.45 AR(16" barrel, A2 front sight, AR BCG, carbine spring and buffer) I had to remove the extractor and ejector and then open the bolt face up for the 5.45x39 case. The extractor had to be worked too. What I didn't have to do was mess with the gas port.

If you are using the 5.56 bolt, measure the face on it and then measure the 5.45 case. There is something like a .015-.020 difference in size. HTH.
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Old January 25, 2019, 19:10   #35
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Well, here we go again.
To answer this question first the bolt is indeed a 5.45x39 bolt not a 5.56x45/.223.

Made it out to the shop to releave the extractor then releaved my bowels, in my pants, perfect. I failed to employ rule #1, take my morning dump before going all the way out to the shop. Shit happens when your old.

After a shower back out to the shop. I used my small air tool, a pencil type with a sharp pointed diamond bit. Due to the configuration of the extractor the sharp point was required to just hit the back face of the extractor that catches the case rim. This worked out very well and very controllable. The extractor is hard as a wedding cock but the diamond bit did it’s job without over doing it. I only removed a few thousandths, like about 3 or 4, not very much which was surprising. A few reassembles and checks and I was home free. It is important to keep the extractor edge square and sharp, not rounded on the back side.

Testing was positive with no failures to extract or close the bolt fully. Yea!
The M16 carrier was not consistent locking the bolt fully back on the bolt stop when the magazine was empty. Tried the AR15 carrier same thing, not consistent. The only time I have found bolt locking back fully is with the reduced power captured recoil spring mechanism. I like the JP Enterprises captured buffer/recoil spring assembly much better than the standard spring as it eliminates the spong from the standard spring and also provides spring choices to fine tune the assembly. They are not cheap at $134.00 but the benefits are worth it to me. I have no intention to open the gas port any more than .101 in diameter, just because. Accuracy testing and dialing the sights in will have to wait for another day.
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The fear of God is the beginning of wisdom.

Matthew 25:1 thru 25:10 Be ready!

The written word sometimes like poetry is never really finished but merely abandoned.

I live alone in the middle of nowhere with two dogs and a cat, what do you think about that.

The wind blows, the rain falls, the flag snaps its bravery in the dark as two dogs boil for attention at my feet.

Of course it is a true story. You just couldn't make up something like that, no way.

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Old January 25, 2019, 20:58   #36
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Mine purrs...might have had to open port above 0.093" a little. Ballistic Advantage bolt/barrel.

...but no farticulate either.....
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Old February 16, 2019, 22:07   #37
Sagerider
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5.45x39 AR update

The Wolff reduced power recoil spring I ordered arrived! Yea!
I installed it and gave it a go with very good results. The last round out locked the bolt back fully instead of locking on the carrier as it was doing with a standard recoil spring. This of corse all makes sense and my logic is below.

5.45x39 runs about 2,800 FPS depending on barrel length due to a smaller case capacity/powder which means less pressure at the gas port compared to a 5.56x45. Pressure at the breach I imagine may very well be 50 to 60k psi so I am just talking about volume at this point. Keep in mind this is an 18 inch barrel with a rifle length gas tube. Gas port was opened from .082 to .101, rifle runs normally with no indication of over gassing, cases do eject with authority but not overly so.
The reduced recoil spring was just the right touch to ensure the bolt is locked full rearward on the bolt stop. The 5.45x39 is in all purposes a less powerful cartridge than the 5.56x45 so it makes sense again to down size the recoil spring slightly. It works just fine as planned.

So there you have it. Accuracy appears to be very good when sighting in but a more disciplined target session rather than function testing should be a happy event. I did install a Compass Lake .050 wide target front post which I prefer over the standard .070 wide front post.
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The fear of God is the beginning of wisdom.

Matthew 25:1 thru 25:10 Be ready!

The written word sometimes like poetry is never really finished but merely abandoned.

I live alone in the middle of nowhere with two dogs and a cat, what do you think about that.

The wind blows, the rain falls, the flag snaps its bravery in the dark as two dogs boil for attention at my feet.

Of course it is a true story. You just couldn't make up something like that, no way.

Last edited by Sagerider; February 17, 2019 at 01:20.
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Old February 16, 2019, 23:00   #38
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I'm happy that you've worked it all out and it's a GO...

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