AR short stroking

[Mdphotographer]

I bought a DPMS AR at the Dulles Gun Show a couple weeks ago and am having an issue with it any help would be greatly appreciated.I took it to Hap Baker the day after I got it and put 200 round thru it without any issues with the exception of that it was hitting way left.I took it home and gave it a good cleaning with CLP.I took a trip to Camp Perry last week to check out the national matches and took it to the DPMS building there and the guy there said the FSB was canted a bit so he took it next door to the Bushmaster building and they got it aligned for me.I took it back to Hap Baker yesterday and the first two mags ran thru it fine and it was shooting much better.I got it sighted in and started the 3rd mag and it started short stroking.I field stripped it and couldn't see anything wrong with it so I ran the chamber brush in it and a couple dry patches to see if it was fouled and that would help.After re-assembly it was FTE, stove piping, or short stroking.I took it home and disassembled again and I noticed the gas block on top of the bolt was loose enough for me to wiggle it back and forth a bit.I figure since the gas block was loose I was venting gas that should of driven the bolt back.I am just wondering if this could be the only cause or is it more likely that I have another issue now?

 

[blindnoodle]

I just chased a similar problem for about two months... Find a fix and it did it again, find another fix and it happened again... over and over.

Plug the chamber end of the barrel with something, towel, cork, anything. Blow into the muzzle. If air comes out of the gas tube then you're close to having the gas block and gas port on the barrel aligned. Loosen the gas block and test to see how the air is restricted. You'll notice a sweet spot. Tighten your gas block in this sweet spot and locktite the screws. If you got it right you'll be golden. If you don't have it right all that pressure will end up either moving the gas block again, or blowing out the "sealed" end of the gas tube.

With mine I had a crappy gas block. It moved no matter what I did. I eventually tossed the whole gas block gas tube pair and started over. It was a RRA bull barrel gas block, just an FYI.

 

[Russ D]

Sounds like your carrier key has worked it's way loose. A properly staked carrier key will not do this. Also be sure your FSB is tight and the tube is sealing well since they moved it. They may have caused a problem by fixing a problem.

 

[303_enfield]

torque the gas key screws and then staked properly.

 

[hole punch]

...Plug the chamber end of the barrel with something, towel, cork, anything. Blow into the muzzle...

and please post pics of your doing this. i dont know why but it brings a funny picture to mind lol

anyways, sounds like the hol in the barrel isn't lining up with the hole in the gas block. makes sense. it cycled fine until your buddy aligned the front sights. you need gunsmith who can put a gasblock on an AR. quick fix. he can do it while you wait.

 

[Jaybeez]

and please post pics of your doing this. i dont know why but it brings a funny picture to mind lol

anyways, sounds like the hol in the barrel isn't lining up with the hole in the gas block. makes sense. it cycled fine until your buddy aligned the front sights. you need gunsmith who can put a gasblock on an AR. quick fix. he can do it while you wait.

Yeah, it sounds like the problem might be that the hole in the gas block isnt lined up with the hole in the barrel, now that the "cant" has been "fixed".

 

[hole punch]

so what do think JayBeez? manufacturer's defect and needs to be shipped back, or can the hole simply be drilled out or reamed bigger? or do you think it'll all just line back up?

 

[Mdphotographer]

The guy at DPMS told me they just loosened the barrel locking ring and rotated the barrel assembly to the proper alignment then tightened the locking ring back down I believe.I don't think the FSB was touched at all.When I cleaned it after the first trip to the range I DID remove the carrier key for cleaning which I know now was a mistake.I don't have a staking tool should I just use some locktite on the screws or can I re-stake it with a small punch?

 

[blindnoodle]

The guy at DPMS told me they just loosened the barrel locking ring and rotated the barrel assembly to the proper alignment then tightened the locking ring back down I believe.I don't think the FSB was touched at all.When I cleaned it after the first trip to the range I DID remove the carrier key for cleaning which I know now was a mistake.I don't have a staking tool should I just use some locktite on the screws or can I re-stake it with a small punch?

if I understand what you're saying then the feed ramps would have looked canter in the upper and the gas tube would have been bent to hell inorder to go from a gas port at any position other than 12 o'clock into the upper. You would have had much bigger problems... Not to mention the alignment pin on the barrel that slides into the groove of the upper.

 

[Markp]

My DPMS had a similar problem, and I thought it was short stroking as well... While the gas key is the likely culprit, watch the spring on the extractor too.

Actually, in my case it was an extractor problem. I HIGHLY RECOMMEND looking at the extractor. I solved the problem by placing a #60 o-ring around the extractor spring... What a DIFFERENCE. The feed problems nearly all cured with the exception of a mag that now needs tuning.

Mark

 

[lee2]

I think i'd give dpms a call.

 

[LostSoul]

As stated, tighten down the gas key on the bolt carrier, stake the screws, and try again. That's probably all there is your current problem.

 

[Russ D]

My DPMS had a similar problem, and I thought it was short stroking as well... While the gas key is the likely culprit, watch the spring on the extractor too.

Actually, in my case it was an extractor problem. I HIGHLY RECOMMEND looking at the extractor. I solved the problem by placing a #60 o-ring around the extractor spring... What a DIFFERENCE. The feed problems nearly all cured with the exception of a mag that now needs tuning.

Mark

A good Ar should function perfectly as designed. If you need an upgraded extractor just to keep it running you are either running it dry or there is a problem with you weapon. The only time you should need an upgraded extractor is switching between steel case and brass ammo or shooting milsurp stuff.

 

[Mdphotographer]

I tightened the key screws as much as I dared and then with a center punch staked them as best I could if that doesnt work and they work loose again should I try some locktite?

 

[gunrunner]

Did you build this gun or buy the carrier elsewhere and put it in yourself? Because as far as i know DPMS as well as all other major manufacturers stake their gas keys. I know Dpms sells carrier kits that of course are not staked. This just seems a bit strange to me. Also, there is no way for the barrel to be "rotated" as stated before. The barrel has a lug that locks into the upper receivers groove. The FSB or gas block as you put it could me moved or misaligned with the hole in the gas tube. To me this is most likely the cause of the Short stroke. One way to check it is to remove the gas block and look at the carbon print on the barrel. If it needs to move to be aligned properly a gunsmith can "drift" the hole and get better alignment. The sharp pressure curves associated with the stoner system require the openings in the gas block and barrel to be perfectly aligned or you will have constant issues.

Another question is what length is the upper? Carbine, Middy or A2? And by the way unless your switching your carrier over to a piston driven system. You should NEVER need to remove the gas key. Make sure its secure. Hope this helps.

 

[Russ D]

DPMS and RRA BCG's aren't staked worth a crap. I restaked mine. Improperly staked BCG's will work loose.

 

[Markp]

A good Ar should function perfectly as designed. If you need an upgraded extractor just to keep it running you are either running it dry or there is a problem with you weapon. The only time you should need an upgraded extractor is switching between steel case and brass ammo or shooting milsurp stuff.

Should and does are two different things...

Bottom line is that the thing failed to work properly with whatever spring was in the DPMS bolt and works perfectly with the "o-ring" fix. I didn't come up with the fix and I'm not the first person to note that a weak extractor spring can be a problem.

I assure you that I am not running it dry and yes, there is a problem, whatever spring was in the extractor was not properly doing it's job. The proper fix is to replace the extractor spring with one that works properly and not the o-ring fix, I decided to do the o-ring fix to test the theory, the proper spring is on the way.

I also believe that it should not matter what ammo you feed it. Your rifle should work with the top of the line ammo as easily as it works with crap wolf ammo or mil surplus. I fire brass, steel, mil surp all out of my AR and yes, I expect the rifle to fire it all... My RPK does, my SKS does, my 8mm Mauser does, my Mosin does, my springfield XD does, and as a matter of fact all my guns that I keep will fire anything I feed them within reason (i.e. non-defective ammo.) I have only given up on one gun so far, it was a springfield 1911, it just was a picky bitch... gunsmiths couldn't fix it, I couldn't fix it, I traded it in on the XD and couldn't be happier.

Mark

 

[Russ D]

The issue with steel case is it doesn't expand as quickly as brass. This leads to more crap in the chamber. If you then switch to brass without cleaning your chamber the brass will quickly expand and get stuck on all the crud left behind from shooting the steel. This is the issue the upgraded extractor can help avoid. My point was the bolt was improperly assembled if the spring it came with was not extracting properly. Not that your fix wasn't the best course of action. I also agree with you, a good Ar should run with any ammo it is designed to shoot. If your gun doesn't run steel it's not a good gun. It's the switching between the two without cleaning the chamber in between that is an issue.

 

[Mdphotographer]

I bought the gun complete from a vendor at the last Dulles Gun Show.The FSB was not touched when they fixed the sight in problem there were NO evidence of ANY kind that the FSB pins have been touched.When I disassembled it after my first trip to the range I removed the carrier key not knowing I wasn't supposed too.As was explained to me by the DPMS rep is that when the barrel locking lug is tightened the barrel assembly can rotate a touch if you aren't careful.It was out of line enough to throw off bullet placement by12" or so at 50yds with the windage zeroed.(it doesn't take much).I did some more searching this evening and found this.

http://www.ar15armory.com/forums/AR15-Troubleshooting-Tec-t5332.html

I fired 2 full magazines out of my AR after the front sight issue was addressed with no issues it was the 3 or 4th round on the third magazine that the short stroking began.It seems to me that this is an issues of the carrier key working loose to the point that there was too much pressure loss to fully cycle the bolt.Moreover if fixing the sight issue had been the route cause of the short stroking due to the gas block in the FSB being misaligned then the short stroking would of happened earlier then in the 3rd magazine.In my original post I mentioned the gas block on top of the bolt unaware that the proper name was carrier key.The gas block on the barrel has not been touched since manufacture as far as I know.

 

[Russ D]

Stake that sucker and be done with it. Or go to Midway and get a good Daniel Defence BCG for 150$ and never worry again. Good staking and a full auto heavy carrier.