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Old October 22, 2019, 10:06   #1
TheOtherTinMan
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AR build not cycling

Yeah yeah, I know, but anyway...

Slapped a new upper on a lower I put together. Took to the range, it fires, ejects, but fails to load next round. Bolt goes home but fails to strip next round out of mag.

Using Magpul mags, upper is .223 wylde, using US made green tip.

Manual charging works fine, and locks back on empty mag. Brand new upper.

So... Where to begin?

Should I put the upper on a different lower to see if anything changes? And/or put different upper on the lower to check that? Then go from there?

The upper is a 20" free floated barrel with low profile gas block under mlok rail. I'm hoping I don't have to start disassembling stuff to troubleshoot this. Just trying to figure out a workflow to follow instead of cursing and swearing.
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Old October 22, 2019, 10:16   #2
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First try different mags then, if you have another functional AR, yes swap the uppers and lowers around. That will help immensely in pointing you in the correct direction.
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Old October 22, 2019, 10:25   #3
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20-inch probably isn’t OVER gassed.

First order of business is determine whether there are gas leaks. Misaligned gas tube would be my first point of exam.

Don’t be afraid to disassemble an AR. If you can put a chain back on your bike, you can assemble an AR.
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Old October 22, 2019, 10:31   #4
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20-inch probably isn’t OVER gassed.

First order of business is determine whether there are gas leaks. Misaligned gas tube would be my first point of exam.

Don’t be afraid to disassemble an AR. If you can put a chain back on your bike, you can assemble an AR.
I'll swap lowers, that should identify if it's an upper or a lower issue, right? If it's still happening with a lower that I know works otherwise, then I would check the gas tube? Those tubes look almost like flex hose, am I just checking at the gas block and the upper receiver face?

Could it be my buffer spring is weak? I really really really don't want to hear about having to enlarge the gas port... Unless that can be done with a ryobi cordless...
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Old October 22, 2019, 10:49   #5
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Partial cycling it typically a gas issue as WEG said, you simply aren't getting enough. If by chance your gas block is adjustable that is the most obvious starting point, as simply adjusting it more open can help. He mentioned pulling it apart. To take that a step further get the gas block off and see where the gas marks are inside the gas block in reference to the gas port. There should be burn marks if the 2 aren't aligned. If they are you can either enlarge the port, or attack it the other way by lightening the reciprocating mass (real "lighter buffer or carrier) or by using a weaker main spring. You might also want to check your gas key on the BCG to ensure it's tight and not leaking.

In a 20 in I think I'd give it more gas by opening the port up first and see what that does for you, but if you have other mainsprings available swapping those out can be a quick and simple fix.
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Old October 22, 2019, 11:57   #6
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Partial cycling it typically a gas issue as WEG said, you simply aren't getting enough. If by chance your gas block is adjustable that is the most obvious starting point, as simply adjusting it more open can help. He mentioned pulling it apart. To take that a step further get the gas block off and see where the gas marks are inside the gas block in reference to the gas port. There should be burn marks if the 2 aren't aligned. If they are you can either enlarge the port, or attack it the other way by lightening the reciprocating mass (real "lighter buffer or carrier) or by using a weaker main spring. You might also want to check your gas key on the BCG to ensure it's tight and not leaking.

In a 20 in I think I'd give it more gas by opening the port up first and see what that does for you, but if you have other mainsprings available swapping those out can be a quick and simple fix.
What tools are needed to take off the gas block?
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Old October 22, 2019, 12:04   #7
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Those tubes look almost like flex hose, am I just checking at the gas block and the upper receiver face?
Tube could be damaged somehow. Damage may be hidden by the gas block, so you won't know unless you drive the pin out and examine the portion of the gas tube that has to line up with the port-hole in the gas block. When you put it back together, you will get a good sense of whether things are lining-up, or whether there is some spot where gas will escape.

Check your carrier key too. Even when properly installed, some leakage between the key and the carrier is common. We're looking for gross leaks or blockages. Don't be concerned if there is evidence of some small leakage.

I've had rifle length uppers that simply didn't like factory ball ammo, in the sense that they would not reliably lock back, but would cycle from the magazine. Yours seems to be the opposite symptoms - which I think is weird.

The bolt/carrier assembly has to travel FARTHER rearward to pick up a fresh round than it does to lock back. Often, the guns that won't pick up the next round are cycling so fast that the ammo-stack cannot rise in time to be picked up by the bolt. We usually don't see that in rifle-length systems.

Trying the upper on another lower won't hurt anything. But, I'm not sure it will tell you everything you need to know. If this upper does work ok on another lower, what does that tell you about how to make it work with the present lower?

Are you SURE the magazine was fully seated when you had the bolt-over-base failures? It takes very little too-low-magazine condition to encounter bolt-over-base.
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Old October 22, 2019, 12:07   #8
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What tools are needed to take off the gas block?
You have to get access to the gas block. So remove the handguard rail.

Knock the roll-pin out with a punch. It helps to have a titty-tip punch for removing roll pins. Also helps to have a starter punch for installing roll pins. Expect to bugger the pin. Don't take it apart unless you are prepared to replace the roll pin every time you do it. Once you get the hang of it, you will destroy fewer roll pins.

Brownells sells titty-punches and starter-punches for AR-type guns. Worth buying if you have any notion that you will ever tinker with AR's.
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Old October 22, 2019, 12:10   #9
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I have never seen a gas tube that looks like a flex hose. Pics???
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Old October 22, 2019, 12:13   #10
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Thanks for help. I'll round up some punches, and take a trip to the range tomorrow (soaking wet right now from the severe storms we just had), check with different mags, swap lowers around, then back to the bench to tackle the gas block.
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Old October 22, 2019, 12:15   #11
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I have never seen a gas tube that looks like a flex hose. Pics???
I meant compared to a FAL or AK, it looks like a snakey aluminum tube thingy rather than a straight metal tube. It's not a total bubba gun with zip ties and mcdonald straws lol.
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Old October 22, 2019, 12:27   #12
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I meant compared to a FAL or AK, it looks like a snakey aluminum tube thingy rather than a straight metal tube. It's not a total bubba gun with zip ties and mcdonald straws lol.
Not sure if you can see what I meant, there's a bend in the gas tube:
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Old October 22, 2019, 12:34   #13
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The bend should be there...

Don't straighten it out...

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Old October 22, 2019, 13:15   #14
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All AR's have a bend in the gas tube.

Depending on how the gas block is attached to the barrel, you will need a wrench that matches the fastener to loosen the set-screws or clamp screws. Don't be surprised if you need to use considerable heat to get it to let go. I always splooge extra blue loctite on the screws when I put it back together. Then I end up having to take it back apart. Lots of heat to get my mess to let go. Remember the gas block is still hot enough to burn you real bad, even if its not glowing red. If it starts falling off the gun, or off the bench, while its hot, just let it fall.
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Old October 22, 2019, 13:44   #15
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If it starts falling off the gun, or off the bench, while its hot, just let it fall.
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Old October 22, 2019, 13:45   #16
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First try different mags then, if you have another functional AR, yes swap the uppers and lowers around. That will help immensely in pointing you in the correct direction.
Ding, ding, ding!!

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"How we burned in the prison camps later thinking: what would things have been like if every security operative, when he went out at night to make an arrest, had been uncertain whether he would return alive and had to say good-bye to his family? Or if during periods of mass arrests people had simply not sat there in their lairs, paling with terror at every step on the staircase, but had understood they had nothing to lose and had boldly set up in the downstairs hall an ambush of half a dozen people with axes, ham- mers, pokers, or whatever else was at hand. . . . The Organs [police] would very quickly have suffered a shortage of officers . . . and notwithstanding all of Stalin‘s thirst, the cursed machine would have ground to a halt." - A. Solzhenitsyn, Gulag Archipelago
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Old October 22, 2019, 13:46   #17
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Lube it up. A lot.
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Old October 22, 2019, 13:50   #18
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^

Yes.

But it isn't even picking up a round out of the mag.
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Old October 22, 2019, 13:56   #19
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Bolt retracting fully ?

Correct buffer for the recoil tube ?

Wrong length screw on a rifle stock ?

Short recoil tube ?


ETA: if it is ejecting, but not picking up a round, it is usually not the magazine, or the gas system.

It is some 25 cent part shutting down the machine.


..........................................
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Old October 22, 2019, 14:44   #20
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^

Yes.

But it isn't even picking up a round out of the mag.
Because its short stroking. Seen it before on new dry AR15. After running wet for sever mags it didnt need to run so wet.

Now this could well be undergassed but for a new build run it wet fir a while and see if the problem doesnt just go away for good.
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Old October 22, 2019, 14:50   #21
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My first AR, when it was brand spanking new, wouldn't cycle properly with cheap 55grn 5.56x45. We ran some hotter 5.56 through it and it ran fine. Apparently mine needed to be shot a bit to break it in. It now digests everything I throw at it.
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Old October 22, 2019, 14:57   #22
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What tools are needed to take off the gas block?
The freefloat tube and most low-pro gas blocks are held in place with allen screws. Very few if any low-pros I've ever seen were pinned in place, but it's possible. Most have several set screws in the bottom, some clamp. For the FF tube a few are threaded onto the barrel nut, but most clamp onto the barrel nut with a couple of allen screws, and a very few use torx, but my money is on allen screws for both.
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Old October 22, 2019, 15:28   #23
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Bolt retracting fully ?

Correct buffer for the recoil tube ?

Wrong length screw on a rifle stock ?

Short recoil tube ?


ETA: if it is ejecting, but not picking up a round, it is usually not the magazine, or the gas system.

It is some 25 cent part shutting down the machine.


..........................................
I noticed it has a bit more thread showing on the buffer tube at the receiver. Found out when I collapsed the stock all the way then couldn't get it to extend without another pair of hands yanking on it. My Colt doesn't have that problem, shows fewer threads there.

Not sure if that's even relevant to anything, as I know nothing about ARs except they are chapping my arse.
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Old October 22, 2019, 15:29   #24
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The freefloat tube and most low-pro gas blocks are held in place with allen screws. Very few if any low-pros I've ever seen were pinned in place, but it's possible. Most have several set screws in the bottom, some clamp. For the FF tube a few are threaded onto the barrel nut, but most clamp onto the barrel nut with a couple of allen screws, and a very few use torx, but my money is on allen screws for both.
Looking at it with my squinty eye it looks like that's how it is. So hopefully shouldn't be too big of a deal to take it apart and spank it like an AK - oh, wait...
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Old October 22, 2019, 15:49   #25
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What recoil buffer are you using?
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Old October 22, 2019, 15:53   #26
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I'll swap lowers, that should identify if it's an upper or a lower issue, right?
Yes.
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Old October 22, 2019, 16:05   #27
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What tools are needed to take off the gas block?
LEAVE THE GAS BLOCK ALONE. Start by trouble shooting the lower first.

Measure the length of your buffer, and buffer spring.

Measure your buffer and buffer spring length. Compare.

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Old October 22, 2019, 16:08   #28
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I noticed it has a bit more thread showing on the buffer tube at the receiver. Found out when I collapsed the stock all the way then couldn't get it to extend without another pair of hands yanking on it. My Colt doesn't have that problem, shows fewer threads there.

Not sure if that's even relevant to anything, as I know nothing about ARs except they are chapping my arse.
Your receiver extension ("buffer tube") may be commercial (larger) diameter, and (slightly smaller) mil-spec..... it has nothing to do with your cycling issues.
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Old October 22, 2019, 16:23   #29
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The freefloat tube and most low-pro gas blocks are held in place with allen screws. Very few if any low-pros I've ever seen were pinned in place, but it's possible. Most have several set screws in the bottom, some clamp. For the FF tube a few are threaded onto the barrel nut, but most clamp onto the barrel nut with a couple of allen screws, and a very few use torx, but my money is on allen screws for both.
yep, might be misaligned and covering the gas port. Done that

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LEAVE THE GAS BLOCK ALONE. Start by trouble shooting the lower first.

Measure the length of your buffer, and buffer spring.

Measure your buffer and buffer spring length. Compare.

And yep. Never done that because I know better.
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Old October 22, 2019, 16:37   #30
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What recoil buffer are you using?
I have no idea, actually. I do believe it's "mil-spec"...

Wait... That would be the tube, not the buffer...

See? I know nothing about ARs.
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Old October 22, 2019, 16:48   #31
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And, once again, really appreciate all the help, guys.

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Old October 22, 2019, 16:52   #32
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I have no idea, actually. I do believe it's "mil-spec"...

Wait... That would be the tube, not the buffer...

See? I know nothing about ARs.
Commercial tube is thicker with a larger OD than mil spec, but the ID is the same. Don't get off in the weeds
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Old October 22, 2019, 17:19   #33
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If buffer is milspec carbine likely to have no markings. If an H1, H2, H3, etc should be stamped on face of buffer. If you have a collapsible stock odds are buffer tube is correct length. Did you assemble the upper, a friend, bought from discussion group or commercial vendor? I would lubricate the crap out of it and run some hot and heavy loads to see if that lossens it up a bit. If not would pull handguard and examine gas block to ensure gas hole in block and barrel are properly aligned. Often the dimples in some barrels do not line up with screws in some blocks.

If barrel is not dimpled and block is pushed all the way against the shoulder then that may be issue as usually there is a space the thickness of a milspec handguard cap between the shoulder of barrel and rear of gas block. Have seen many people shove gas block till makes contact with shoulder, tighten grub screws and cut off 30% of gas flow due to misalignment. Since gas blocks are generally hidden under handguard I usually scribe a small line in shoulder of barrel and top rear of gas block to ensure the two are "clocked" properly before snug the grub screws and measure from shoulder to center of gas port in barrel then from rear of gas block to center of gas port on and do elementary school math to ensure the two are aligned in that aspect as well. Years ago I cut an old front handguard cap so that it would slip over a barrel then could push block till stops, snug one grub screw and slide the handguard cap out but same thing can be done with set of feeler gauges.

1. Lube heavy & shoot some hot 77 grain loads through rifle. Use more than one brand and type of magazine.
(If they work but then the 62 grain still give issue look at buffer weight)

2. Pull handguard and examine gas block. (Number 1 for me as can do in shop)

3. Doubt lower is an issue unless magazine is not locking in correct position but you said bolt was locking back on empty magazine.

4. If pull gas block examine gas tube for kinks, if able to blow air through and correct length. Have seen carbine length tubes used on mid length rifles. Measure your gas length and don't assume your 20" is rifle length till measure. I have a 20" that is mid length and one that is rifle plus one inch.

5. (Or 2.) When swap lowers if upper works properly would buy a name brand bolt catch and replace. Have seen Chinese lower parts kits that were out of spec. I always buy DPMS lower parts kits for milspec builds as found them to be 100% consistent and well priced.
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Old October 22, 2019, 17:54   #34
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Don't get off in the weeds
...... and here comes Huey!
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Old October 22, 2019, 18:16   #35
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...... and here comes Huey!
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Old October 22, 2019, 19:30   #36
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Because its short stroking...
Good point.

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Old October 22, 2019, 20:26   #37
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Good point.

… and lotsa' lube isn't going to fix it if the builder used a rifle length buffer and/or spring in a carbine length recoil tube, which is common among novice builders and easily rectifiable. There may be other issues, but this block should be checked first IMHO.

The hole in a gas block is very large compared to the gas port. A misaligned gas port isn't that common (most common when installed low profile gas blocks on barrels manufactured to accept a fixed sight block w/ handguard retaining ring).

I also don't subscribe to the utilization of heavy applications of lube for an AR build. Lube should only be applied to metal to metal contact points, and not in excess. The metal to metal contact points with an AR are minimal. Excess lube is redundant, and only exacerbates the inclusion of contaminates in an already dirty direct gas impingement gas system.
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Old October 22, 2019, 20:30   #38
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… and lotsa' lube isn't going to fix it if the builder used a rifle length buffer and/or spring in a carbine length recoil tube.

.....
Presactly.


If more lube overcame short-stroking, a lot of FALFilers wives would be smiling more.



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Old October 22, 2019, 20:41   #39
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Presactly.


If more lube overcame short-stroking, a lot of FALFilers wives would be smiling more.



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Soft ball pitch.... you knocked it out of the park.
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Old October 22, 2019, 20:53   #40
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Originally Posted by lockjaw View Post
… and lotsa' lube isn't going to fix it if the builder used a rifle length buffer and/or spring in a carbine length recoil tube, which is common among novice builders and easily rectifiable. There may be other issues, but this block should be checked first IMHO.

The hole in a gas block is very large compared to the gas port. A misaligned gas port isn't that common (most common when installed low profile gas blocks on barrels manufactured to accept a fixed sight block w/ handguard retaining ring).

I also don't subscribe to the utilization of heavy applications of lube for an AR build. Lube should only be applied to metal to metal contact points, and not in excess. The metal to metal contact points with an AR are minimal. Excess lube is redundant, and only exacerbates the inclusion of contaminates in an already dirty direct gas impingement gas system.
I normally piss on mine to neutralize powder and corrosion in the gas system.
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Old October 22, 2019, 21:07   #41
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I normally piss on mine to neutralize powder and corrosion in the gas system.
Have you been hanging out with Russian Bot 5791? That is what his great grandmother would have done.
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Old October 22, 2019, 21:51   #42
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If you’re gonna piss on it, use a water soluble lube.

Astro-Glide is a good pick. If you can find some Vagisil in the hall closet, that will work too.
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Old October 22, 2019, 22:27   #43
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Originally Posted by lockjaw View Post
… and lotsa' lube isn't going to fix it if the builder used a rifle length buffer and/or spring in a carbine length recoil tube, which is common among novice builders and easily rectifiable. There may be other issues, but this block should be checked first IMHO.
Hmm. The upper was ordered and put together by a local smith. I had a CMMG lower and DPMS lower parts kit. I put the lower together, I bought a collapsible stock at the smithy's store, I believe the buffer was ordered with the upper... can't remember if an off the shelf Magpul stock includes the tube, buffer, and spring, or just the stock...? So maybe what you mentioned is what I did.

I did notice today it's a bit harder to pull back the charging handle on this build than on my Colt, so I was thinking maybe the spring is a bit too stout or maybe it's too cramped in the tube (buffer/spring too long for the tube?)...
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Old October 22, 2019, 23:58   #44
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… and lotsa' lube isn't going to fix it if the builder used a rifle length buffer and/or spring in a carbine length recoil tube....
Yep.
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Old October 23, 2019, 04:37   #45
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>>I put the lower together<<

Check the disconnect to hammer free play.

Several of the AR disconnectors that Ive seen lately have been too long. After the round has been fired, and the carrier is moving to the rear, if the hammer strikes the disco too early it slows down the action causing a short stroke. Compare the disconnect to hammer free play in the Colt.
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Old October 23, 2019, 07:06   #46
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Maybe we should have asked earlier: do you have another ARq5 that runs well? Swap uppers and see if problem follows the upper or lower.
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Old October 23, 2019, 07:29   #47
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How many coils on the buffer spring?
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Old October 23, 2019, 12:27   #48
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Maybe we should have asked earlier: do you have another ARq5 that runs well? Swap uppers and see if problem follows the upper or lower.
It's the first thing that Mike asked him in the first response.

not sure we've heard back on this...
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Old October 23, 2019, 13:36   #49
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I've had the same problem with cheap gas blocks.

I have used the .936 gas blocks on heavy barrels.

The diameter of the heavy barrel created a distance from the outer most surface of the barrel directly south of the gas block where the gas tube comes out of the gas block surface was just a bit longer than the distance from the bottom of the gas tube to the .936 diameter surface of the gas block.

Result: cocked gas block. Solution; I cut a channel in top of barrel to allow clearance under gas block. I also took a dremel with a round burr and funneled the gas hole on the .936 diameter surface.

I also laid the upper, on it's pictanny rail, on a Blanchard ground surface which extended to the pictanny rail of the gas block to get them aligned and on the same plane. You may have to use gauge blocks to align different plane gas blocks.

Result is the heavy barreled Wylde 26 inch cycles and loads fine as frogs hair!!

I am working on a 6.5 Grendel with the same problem and same cheap style gas block.

Accuracy, I didn't notice any difference but results may vary.

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Old October 23, 2019, 13:47   #50
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At the range. First, I used a USGI mag (green follower). Got two shots but it failed to strip the third. Have not been able to repeat, now fails to strip the next round.

Put a Colt lower on it - same problem.

Put Colt upper on the new lower, no probs with USGI or Magpul mags.

So either a gas problem, or I have two carbine buffers?
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