PDA

View Full Version : new AR cycling issues


hokey45
February 25, 2017, 19:24
I just put together an AR15 that will not cycle the bolt all the way. It will either pull the case halfway out and stop or eject the spent case but not go back far enough to strip the next round off the mag. It's a 20" fixed stock rifle. I have checked to make sure I have the correct spring and buffer. I have swapped the bolt with another gun that works and it functions fine. I have checked the gas block for alignment and the tube for obstructions/debris. I have tested it with Federal 55 grn and PMC 62 grn. I have tried 3 different brand magazines that all work in my other guns.
Looking at spent brass I do see some consistent scratches on the case neck and shoulder. Would a rough chamber cause the issues I'm having?

BearNAM
February 25, 2017, 19:40
Gas rings on the bolt?

yellowhand
February 25, 2017, 20:02
Not enough gas, gas port blocked or too small

But first, take a chamber brush, chuck it into a short section of cleaning rod, dip it in hoppes and spin/clean the hell out of the chamber.

Stoney
February 25, 2017, 20:16
did you oil that hell out of it? new ARs like lots of oil.

hokey45
February 25, 2017, 21:29
Gas rings on the bolt?

Took the bolt apart. Gas rings ok. Put the bolt in another AR that worked and it still worked. Took the bolt out of a working AR and put into my gun still didn't work.

rbgonoles
February 25, 2017, 21:32
What kind of stock? A1 or A2? If it's he shorter A1 did you use the long screw?

hokey45
February 25, 2017, 21:32
Not enough gas, gas port blocked or too small

But first, take a chamber brush, chuck it into a short section of cleaning rod, dip it in hoppes and spin/clean the hell out of the chamber.

Yes it seems like not enough gas. Didn't measure the diameter of the hole in the barrel. Blew out the gas tube, tried another gas block, checked the alignment, still the same problem.

I'll try the chamber brush trick and see if it works.

hokey45
February 25, 2017, 21:34
What kind of stock

Magpul MOE fixed stock. Rifle length buffer tube with rifle spring and buffer.

hokey45
February 25, 2017, 21:37
What kind of stock? A1 or A2? If it's he shorter A1 did you use the long screw?

Magpul. Don't remember if the screw came with the stock or not. If the screw is too long I could see it limiting bolt travel but wouldn't that also keep me from pulling the bolt back far enough to manually load it?

hokey45
February 25, 2017, 21:39
did you oil that hell out of it? new ARs like lots of oil.

Oiled the spring and bolt but I'll try a heavier coating next time.

badzero
February 26, 2017, 00:40
Had this exact problem a couple of years ago, ended up having to run a reamer through the chamber which cleared up the problem, Armalite barrel.

Bertellione
February 26, 2017, 01:22
[QUOTE=hokey45;4380082]Magpul. Don't remember if the screw came with the stock or not. If the screw is too long I could see it limiting bolt travel but wouldn't that also keep me from pulling the bolt back far enough to manually load it?[/QUOTE

The longer screw I think would just dig into the back of your buffer, you would notice it. What type of gas block are you using? Just in case maybe gas block miss alignment I shave a tooth pick down to the size of the gas hole then cut off before installing the gas block. When it is all lined up the tooth pick will go up and down when you put the barrel at 12 and 6. The tooth pick should up and down. When it slides free it time to set your gas block then push a cleaning rod to break both pieces out

Bertellione
February 26, 2017, 01:24
Had this exact problem a couple of years ago, ended up having to run a reamer through the chamber which cleared up the problem, Armalite barrel.

Who's barrel is it PSA stainless barrels are known to need to be reamed.

Bertellione
February 26, 2017, 01:28
Never shoot a rifle with out cleaning the bore and polishing the chamber

hokey45
February 26, 2017, 06:31
AR Stoner barrel. I'll try cleaning the chamber aggressively and see if that helps. If the chamber needs a pass with a reamer I'll just return the barrel to the vendor and buy something else.

Gas block was a set screw low profile. Marked the centerline on the barrel and the gas block to line them up. Also measured the distance from the shoulder to the gas hole on the barrel with a caliper and measured the same on the gas block to make sure it wasn't off lengthwise. Did the same with another brand gas block. Barrel had divot machined in for one of the set screws, this didn't move the gas block off center when tightened up.

When you say polish the chamber what method do you use? I had the idea I could put an extension on a spent case and spin it in a hand drill with some compound.

0302
February 26, 2017, 14:08
i had same problem with a set screw aluminum gas block, took that pos off & got a steel clamp model problem solved. the set screw was a leaker.

Trypcil
February 26, 2017, 14:30
A new assemblage - cycle the bolt many times with a oil/grease, flush with triflow or whatever, reassemble bcg, re oil/grease, cycle, flush, repeat many times - shoot, to see if the problem goes away - simply taking the edges off, perhaps!

hueyville
February 26, 2017, 15:21
(trim)
But first, take a chamber brush, chuck it into a short section of cleaning rod, dip it in hoppes and spin/clean the hell out of the chamber.

Many new barrels stored with heavy oil, grease, cosmoline, etc. Can give a quick squirt, pass with brush and looks good but enough still in chamber that when rifle fires heat melts just enough to turn the stuff still left into hot glue. Adding some oil can exacerbate the issue as it mixes with the goo and just makes more sticky mess.

Clean the crap out of chamber, clean it again, oil BCG and other moving parts but shoot with chamber dry and see what happens. First time its run, like a rifle that slings oil like a 70's Harley Shovelhead with 100k miles on original set of seals for first few rounds but don't oil up the chamber or bore.

i had same problem with a set screw aluminum gas block, took that pos off & got a steel clamp model problem solved. the set screw was a leaker.

Seen skelotonized steel and aluminum gas blocks out of round or become out of round when installed and set screws are over torqued. If cleaning chamber really good and shooting rifle wet doesn't free it up look for leaking gas block.

Stoney
February 26, 2017, 15:40
you said rifle stock, had the same problem with one, it was the long rifle buffer, put in a carbine one and it was GTG.

yellowhand
February 26, 2017, 15:48
Huey reminded me, when I say a short section of rod, chuck it into an electric drill to spin/clean the crap out of the chamber!
Just keep it wet while doing it.:D
I've fixed a lot of friends AR's that had these issues doing this.

M90A1
February 26, 2017, 20:01
you said rifle stock, had the same problem with one, it was the long rifle buffer, put in a carbine one and it was GTG.

Maybe you could explain what you did here with a little more detail. If you try to use a carbine buffer in a rifle receiver extension, you're going to have big problems with the BCG hitting the lower receiver where the extension mounts. Maybe I misunderstood?

nopec
February 26, 2017, 20:19
Does the gas block / front sight base clamp on or pin on? Is it on correctly? Lube the hell out of the bolt, carrier and upper. Also, get ye some good hot mil spec 5.56 ammo.

hokey45
February 26, 2017, 21:24
Set screw gas block. Going to order a clamp on gas block (I don't think it's the gas block but...) and a chamber brush tomorrow. Will try the scrub chamber and prodigious lube everything else technique and see what happens.

Been shooting Federal bulk 55 grain and PMC 62 grain.

If it is a rough chamber would steel case act any different?

hokey45
February 26, 2017, 21:28
slings oil like a 70's Harley Shovelhead with 100k miles on original set of seals.

I like the analogy:wink:

machinegunner
February 26, 2017, 21:28
Just saw this but. What is new about an AR not cycling?

lysanderxiii
February 26, 2017, 21:32
Set screw gas block. Going to order a clamp on gas block (I don't think it's the gas block but...) and a chamber brush tomorrow. Will try the scrub chamber and prodigious lube everything else technique and see what happens.

Been shooting Federal bulk 55 grain and PMC 62 grain.

If it is a rough chamber would steel case act any different?
Yes, worse.

hokey45
February 26, 2017, 21:32
Huey reminded me, when I say a short section of rod, chuck it into an electric drill to spin/clean the crap out of the chamber!
Just keep it wet while doing it.:D
I've fixed a lot of friends AR's that had these issues doing this.

I wrap 0000 steel wool on a dowel rod and chuck in a drill to clean shotgun barrels.

Getting me a chamber brush tomorrow.

hokey45
February 26, 2017, 21:33
Yes, worse.

Okay won't try that.

gunshooter
February 26, 2017, 22:14
I have the same cycling issues with a couple of builds as well.

I made the mistake of buyin the cheap set screw gas blocks as well.

I am going to:

Remove the gas block from the barrel

check the alignment of the gas tube port to the block gas passage and perhaps run a drill through gas block into gas tube to create uniform gas passage

take some permatex sealant to seal gas tube to gas port or drill passage through gas block and install set screw to force gas port of tube against gas block tube bore

perhaps do a light permatex seal of gas block to bore as well around the top of the barrel around the gas port.

I am not going to enlarge the barrel port size.

I believe I am losing the pressure do to the gas blocks all being cheap discount chinese crap

Why go through this, well I want to determine the causes of the faults and correct them and the gas blocks fit the builds pretty well.

I was able to get the rifles to recoil properly by trimming the springs but that is just a stop gap measure.

The gas coming through seems to be about baby fart force with very light recoil.

The barrels are a 24 inch wylde heavy, a 6.5 Grendal 20 inch heavy and a 16 inch 300 black out.

I can't wait to get back to building fals!!!:tongue:

TerryN
February 26, 2017, 23:46
If you haven't resolved this yet, try polishing the chamber as noted earlier. Many inexpensive barrels have REALLY rough chambers. If that doesn't solve the problem, try applying a light coat of blue Loctite on the gas block seat area of your barrel, then align and tighten it. Allow the Loctite to dry and then test fire the gun. I had a recent build that wasn't getting enough gas, and it turned out the be the cheap Chinese gas block I used. It was too large on the ID to allow a good gas seal. I trashed the cheap as block and replaced it with a decent quality American part, and the rifle worked perfectly!

Stoney
February 27, 2017, 00:17
I used a carbine buffer with the rifle spring in the rifle tube, had a spare and tried it, no problem

hueyville
February 27, 2017, 06:51
Certain parts are not to be skimped on. Bolts, bolt carriers, gas system parts are the heart of the rifle. A bargain barrel can be made to work usually, if terribly oUT of spec seller should replace. Polish, hone, touch-up chamber, drill out port, etc. Furniture can be force fit. But a decent receiver set and the moving and pressure parts need to be real "milspec" not chinese milspec equivelent. Weight saved on a lightweight gas block can bite you. Wow! I just saved another ounce on my rifle! Have found some good bargain keylock handguards. Found good supplier for milspec buffer tube and stock complete groups. (Buffer and springs go in spare parts kits) But all gas blocks, gas tubes, BCG's, receiver sets are worst case first quality cosmetic blems.

See if you can find someone with a bore scope so can inspect chamber well. I have an inspection camera that will insert in 30 caliber or larger bore and most chambers. If chamber looks super rough and a super cleaning doesn't smooth out here is another trick. Buy two chamber brushes, second shorten so does not reach throat or be careful with how deep insert. Do not wamt to damage throat. If cleaning aggressively with fluid does not work use some old fashioned Crest toothpaste or fine lapping compound of choice put on chamber brush and spin the crap out of it with cordless drill. Don't overdo but a little abrasive followed by a triple cleaning may fix it. Have used toothpaste on tight 1911 slides, AR bolt carrier groups, rough chambers and more.

BTW. Midway has the Vortex Strikefire II with red or green dot option for $179 with instant free $50 Midway gift card discount applied to sale and free shipping for a $129 to your door price. Anytime I can get a decent optic close to a hundred bucks I add it to pile.

M90A1
February 27, 2017, 11:53
I used a carbine buffer with the rifle spring in the rifle tube, had a spare and tried it, no problem

If that combination works without destroying the lower receiver, you've got a big problem somewhere else. Think about what's happening here. You replaced a rifle buffer that is considerably longer than the carbine buffer and yet your BCG is not hitting the lower receiver upon firing? There's a really good reason for the difference in the length of a rifle buffer and a carbine buffer. Either you are using severely under-powered ammo, your system is severely under-gassed, or you've got a really big gas leak somewhere. That rifle should have destroyed something upon the first shot fired with those parts. Didn't the difference in the length of the two buffers give you pause? :eek: :confused:

I guess I could be missing something, here, but I can't figure out what it is if I am.

KoKodog
February 27, 2017, 12:31
is the gas tube lining up properly with the gas key on the BCG ?

PARA FN FAL
February 28, 2017, 07:40
My Dissipater with a A1 stock doesn't like a full sized buffer so I run a carbine buffer and spring with no problem so far. My fix to the posted problem would be to try this method as it is easy and quick if you have a carbine to swap parts with. If that doesn't do it then I am sure it's the gas block. I have seen a couple where the screws needed locktite and tightening and then the AR pistols they were on ran fine after that.

It makes no sense to me why are carbine buffer would be damaging a AR lower but not a rifle buffer. Mechanically there is no internal difference between a rifle and carbine. Now if you are talking of the buffer beating up the rifle from to much inertia with the buffer that can't be the problem if it isn't getting enough gas for the heaver buffer. I am not saying that I am any kind of AR expert but when I have addressed a under gassed AR15 with a carbine buffer I have seen no sign of excessive wear.

M90A1
February 28, 2017, 08:50
I don't understand how some of you got such severely under-gassed systems, but that must be why you're getting away with using a carbine buffer in a rifle buffer tube. Take your rifle buffer and drop it into the rifle buffer tube, then measure the distance from the mouth of the tube to the buffer. Do the same thing with the carbine buffer in the rifle tube. There will be a considerable difference in the two measurements. That difference will be how much further the BCG can move to the rear upon firing. If everything was right with the gas system, the gas key would smash into the charging handle first and then into the lower receiver where the buffer tube threads in, probably damaging the handle and the receiver. If you can picture that, you will understand my concern over using a carbine buffer in a rifle buffer tube(receiver extension).

There is the possibility that you guys have a problem in your gas systems that don't involve a too small gas port in your barrels.

Took some measurements. There is a 2-5/8" difference in the length of a rifle buffer and a carbine buffer, which means you have the possibility of the carbine buffer traveling that much further into the rifle buffer tube. That means the BCG could also try to move that much further to the rear upon firing. Can anyone see a problem here? I don't think the buffer spring is going to coil-bind and stop rearward travel before something gets torn up. If you've got a rifle where a carbine buffer in an A2 receiver extension doesn't cause any damage upon firing, you've got a rifle with real serious gas system problems.

bigsky
February 28, 2017, 10:22
If your gas block is aligned properly then your gas tube should be aligned to the gas key properly,,, solves that issue,,,,,,easy to tell by carbon footprint if your gas block is leaking,,, cheap set screw ones due leak,,,,i use good quality American made clamp on blocks, align it and clamp it on,, clamp in a vise on a milling machine, pick a spot and drill through the block and dimple your barrel,,i thread for a 4/40 set screw,,, now your locked in place and NO leaking.....your using rifle tube and spring, so probably not an issue,,,BUT,,,, check your buffer spring "wire" thickness,,especially if your spring is from a cheap source,, too thick of wire ads up and will not let your action fully cycle, same with too many coils..............if all that is good,,, sounds like your chamber is too rough holding the cases too long in the chamber after firing,,,,,,,i would try a KNOWN under powered reload which won't blow the case out so violently,,, if it's a rough chamber the lite round will usually cycle.,,, polish your chamber,,,, I've had enough new chambers with these same issues,,,check your bolt/carrier for burrs,, file and polish those areas,,, especially where bolt locking lugs lock up,,,, if you see the tips of the lugs with any dings, file those edges rounded and smooth,,,, rifle may just need to be broken in...

Augdog
March 02, 2017, 01:25
Instead of wasting time on guessing, pull the gas block and check your port size. Here is a reference chart: http://www.tacticalmachining.com/learn/ar-style-rifles/ar-15-gas-port-sizes.html . You will need a index drill bit set, we use a hole gauge set but that is a little excessive to check 1 barrel.

hueyville
March 02, 2017, 08:37
Seen a lot of gas blocks and FSB's used with free float handguards pushed all the way back to full contact with shoulder and no compensation for the front handguard cap being gone. Not only does gas block have to be clocked in correct position it needs to line up in longitudinal direction. If no handguard cap and pushed all the way to contact with shoulder try pushing 0.025" forward, some gas blocks have holes big enough to cover this issue, some don't. Have seldom had to drill gas port on AR 15 unless barrel was shipped without port drilled. 90% of issues resolved were simple alignment or replacement of gas block.

hueyville
March 04, 2017, 13:04
This is a barrel given to me because owner removed factory front sight block to replace with low profile gas block and free float forearm.

http://i64.tinypic.com/4xg5.jpg

Owner, friends and gun shop tried a total of five more thus counting original factory sight tower that did function, six gas blocks didn't including set screw type, a Geissele set screw with single taper pin combination, followed by multiple set screw types till owner gave up and removed barrel all together.

http://i65.tinypic.com/rbw8d1.jpg

http://i67.tinypic.com/2hmj3wj.jpg

http://i68.tinypic.com/2vv9gnk.jpg

Took a fine file and smoothed up all burrs gently, dimpled for the Geissele block they tried and didn't work. Coated entire area around shoulder except immediately at gas pot with red Loctite and installed the gas block given to me with barrel set 0.025" in front of shoulder. Tightened set screws to proper torque settings with calibrated inch/pound torque wrench. Let sit overnight, recut pin slot and drove taper pin in as per instructions. Put on one of my bargain receiver sets with curly gas tube, H2 buffer, take off stock, free float forearm got in a trade because was painted pink and had to refinish, a few clearance Palmetto parts and the little rifle runs 100% reliable with barrel and gas block three different people gave up on.

Cleaning up the dings was important, locating gas block forward of shoulder helped more than anything, filling holes from OEM FST with Bondo, painting with heavy coat of high solids primer, showing some selective use of Scotch Brite Pad, lots of Loctite and patience was all it took to get this factory barrel with under 100 rounds of ammo down bore but three lifetimes of crappy modifications to running like a Swiss watch. Anyone giving up on a barrel just let me know, will pay shipping to fix and get another $200 parts rifle running.

hongkong3
March 05, 2017, 14:49
did you oil that hell out of it? new ARs like lots of oil.


What Stoney said, on new builds I lube the hell out of it and run 50 or so rounds through it. I may look like I just stepped of a oil rig but they do run, this is the very first thing you should try.

M90A1
March 05, 2017, 16:27
I'm having a real problem with the fact that no-one beside myself has commented on the two guys who state they're using carbine length buffers in rifle buffer tubes. Does nobody else have any concerns about this? Am I wrong in thinking they are courting disaster with this combination of parts?

bigsky
March 05, 2017, 21:19
M90a1,,,,,,i had to chuckle at your post, don't go crazy on us,,,,i agree with you,,,i think you made your point very well in your previous posts so felt no need to respond........yes,,a rifle buffer should be in a rifle butt stock along with a rifle spring, .....i would think putting a carbine buffer in a rifle length buttstock and the weapon working is because the spring is coil binding..........spring wire width and amount of coils is very important,,,i think that the wrong spring is a main cause of issues with home pieced together weapons having cycling issues where parts are sourced from various distributors.....beware of Chinese springs...............with the correct buffer there is about 1/2" clearance before the top back of the carrier slams into the top of the buffer tube assembly and starts breaking things, those putting the wrong buffer in are playing a scary or at least expensive game..........those of you doing this should pull your carrier out,,, shove it into your buffer tube all the way to make sure your not flirting with disaster...,

M90A1
March 05, 2017, 21:49
bigsky......interesting theory about the spring coil-binding and averting disaster, but that isn't happening. I just took some measurements and a rifle buffer moves 3.625 inches into the A1-A2 tube before bottoming out, whereas the carbine buffer moves 6.375 inches into the tube before bottoming out, a difference of 2.750 inches. The difference in the length of a carbine buffer and a rifle buffer is, wait for it, 2.750 inches. These measurements are close. This means that a carbine buffer has the potential to move rearward in the upper, 2.250" more than the .50" allowed, before contacting the charging handle and lower receiver.

That was only one spring, but I doubt there is enough difference in the dimensions of any springs out there to make the spring coil bind within the 1/2 inch of bcg travel allowed, before meeting with a really big problem.

This scenario isn't causing me any heartburn, because I know better than to do this, but somebody, somewhere, is going to have real headaches when they try the wrong combination. Someone probably already has.

bigsky
March 05, 2017, 23:26
M90a1..if it's not the spring coil binding,, then i guess there carrier assembly is bouncing around in that 1/2"of free space and either there spring pressure is holding the carrier from hitting the buffer assembly OR the carrier is already hitting.......I've had a replacement spring with thicker wire,,, think about .010" thicker,, can't remember exactly,,over 40 something coils gains about a 1/2",, stopped my carrier from going far enough to the rear,,, caused stove piping and ftf.................i know you weren't exited,,, you just thought we were all sleeping....lol...

bigsky
March 05, 2017, 23:51
I don't have any rifle length ARs,,, so i can't due a comparison on a rifle length,all carbine assemblys,,, I've had two springs basically the same length for one of my ar10,,,,, can't remember coil count being different,, thicker spring would coil bind and not allow enough travel for the carrier to cycle,,, thinner wire spring works perfect,, somewhere around .450" difference in compressed lengths,, which means the spring was coil binding and the buffer was just smashing the spring into a solid mass....just something for all to keep in mind........................op, did you get your weapon sorted out.

Stoney
March 06, 2017, 00:01
after running a bunch of rounds thru it, I put the rifle buffer back in and then run some more thru, it works OK now with the rifle buffer.

hueyville
March 07, 2017, 06:00
after running a bunch of rounds thru it, I put the rifle buffer back in and then run some more thru, it works OK now with the rifle buffer.

Does o.k. mean 100% or acceptible for moment. Mention this all the time but a Tubbs Flatwire spring can be used in rifle, carbine, AR 15 or AR 10 and fix a lot of issues have seen. All AR 10 builds and all nice AR 15 builds get one.

hokey45
March 07, 2017, 13:17
Ok polished the chamber. This did nothing, still short strokes, will eject and recock hammer but not grab the next round off the mag.

Pulled the spring out and compared to a buddy's rifle spring. Coil diameter and number of turns is the same.

Pulled the gas block off again. Little black circle (1/4") around the gas port but does not seem to the leaking around the block. I may try the loctite trick.

I took a 3/32 (0.09375") drill bit and the shank fits snug in the gas port. I MAY have knocked a chip loose from the manufacturing process because I had a little resistance halfway through that gave way when I pushed on it. I looked and cannot find a chip but the bit moves easy but snug through the hole now. I did not drill the hole just stuck the shank end in by hand. Used new bit (no chuck marks) btw.

Will try it again and see it if was a chip in the gas port restricting gas.

Thanks for everyone's input!

notfrommt
March 07, 2017, 13:52
Ok polished the chamber. This did nothing, still short strokes, will eject and recock hammer but not grab the next round off the mag.

Pulled the spring out and compared to a buddy's rifle spring. Coil diameter and number of turns is the same.

Pulled the gas block off again. Little black circle (1/4") around the gas port but does not seem to the leaking around the block. I may try the loctite trick.

I took a 3/32 (0.09375") drill bit and the shank fits snug in the gas port. I MAY have knocked a chip loose from the manufacturing process because I had a little resistance halfway through that gave way when I pushed on it. I looked and cannot find a chip but the bit moves easy but snug through the hole now. I did not drill the hole just stuck the shank end in by hand. Used new bit (no chuck marks) btw.

Will try it again and see it if was a chip in the gas port restricting gas.

Thanks for everyone's input!



What kind of trigger are you using?

M90A1
March 07, 2017, 16:23
Ok polished the chamber. This did nothing, still short strokes, will eject and recock hammer but not grab the next round off the mag.

Pulled the spring out and compared to a buddy's rifle spring. Coil diameter and number of turns is the same.

Pulled the gas block off again. Little black circle (1/4") around the gas port but does not seem to the leaking around the block. I may try the loctite trick.

I took a 3/32 (0.09375") drill bit and the shank fits snug in the gas port. I MAY have knocked a chip loose from the manufacturing process because I had a little resistance halfway through that gave way when I pushed on it. I looked and cannot find a chip but the bit moves easy but snug through the hole now. I did not drill the hole just stuck the shank end in by hand. Used new bit (no chuck marks) btw.

Will try it again and see it if was a chip in the gas port restricting gas.

Thanks for everyone's input!

Check to make sure the gas key on the bolt carrier is tight and not leaking. Once in a while one of the screws will come loose or break, and with the staking, not come out of the recess.

hokey45
March 07, 2017, 21:23
Ok it was a chip or burr in the gas port. Took it out this evening and it ran fine. Thank you everyone for your help!