ok slt will get on here and post more about the problem

Ok I was looking at the gun again this morning and noticed gas tube residue on the bottom of the scope. It's coming out right below the scope behind barrel, it's at the very back between the mag and back of the barrel. So now I'm thinking we need a new gas tube or it wasn't put back together correctly by the previous owner. This would be consistent with a previous post about the gas not building up enough to force the bolt all the way back. I guess we will take it apart and check the gas tube and replace it if needed. What do you think ?

You are going to get some residue in that area no matter what you do or how well you keep your rifle clean. Just because thers some residue there doesnt mean you have a bad gas tube. Besides if the BCG is not slamming all the way forward when you charge it that shouldnt have anything to do with teh gas tube as the problem is occuring even without firing the weapon. If your in the area let me know I would be glad to take a look at it for you !

I worked on a DPMS parts gun the other day that was short stroking. I initially thought it was a buffer/spring issue. I eventually swapped out the bolt carrier with a proven one from LMT. The problem went a away.

I replaced the unstaked suspect key on the original carrier. The front screw was tighter than dick's hatband and the rear very loose. When I pulled the key off I could see obvious evidence of gas leakage. I cleaned it up, degreased it and installed a new USGI key with new screws. I torqued them at 57 in lbs and staked them. It now functions 100%.

Check your gas rings. The gaps might be aligned.

The problem only happens while firing. If you cycle the rounds manually it never happens. This is not a small amount of residue it was a lot. All of my rock river rifles don't do this and I don't ever remember seeing this with my bushmaster.

I will have him contact you Brandon A through PM so you can look at it if we can't figure it out. I'm going to check the gas rings too.

Ah ok !! I thought it was binding when you tried to charge it as well !! That makes things a little different !!

If you are talking about me, he sent me a PM last night and I think we are going to try and hook up this week if he can swing it. I do have single coil and mil spec gas rings we can replace the original with while we are at it if needed !

If you were talking about Brandon"A" he can help you with chopping wood !! Sorry B I couldnt contain myself !!

Yea you the right one sorry to many Brandons on here.

Ok, I didn't read all the possible issues but here is one I witnessed the other day.


The small gas tube on the bolt carrier (not sure official name of tube) had wiggled loose over time. When it's not tight, and it ever so slightly gets off line with the other gas tube and doesn't have enough pressure to blow the bolt back. Make sure you check that very easy fix that we over looked several times after checking all the other more common issues.

Good info will check this. Thanks

Yep, it's called a gas key. If they are loose they won't run. Sometime it's hard to diagnose until you put a wrench on it.

The gas key needs to be "properly" staked to keep this from happening and is teh first thing I check on any AR rifle I buy. If the key isnt properlly staked or not staked at all (many Olly Arms an DPMS are known for this) and you put a lot of rounds down range its not matter of "if" this will be a problem its a matter of "when" will this be a problem.

What staking tool do you use OT ?

I use a big chisel that I dulled on a gringing wheel. I lay the BCG in a vise and give it a goog whack with a ball pein hammer.

That MOAKS tool is supposed to be really nice.

Yeah I have checked out the Moaks tool. I Usually tell guys to contact the manufactuer and make them make it right but its easier, quicker and less of a hassle if I could offer it. I was kind of suprized that some of the lower end rifles have absolutely NO staking on the key !

Could either Brandon or OT post a picture of what I need to look for? My DPMS has been 110% so far, but I'd like to check mine. Thanks, guys

I've seen that too. "just one less X in the column"

Some staking is not substantial enough to do anything. The best staking I've seen is on the the carriers from BCM. Some manufacturers use the top stake method but most side stake these days. Top staking requires a hydraulic press, side staking can even be done in the field with a blunt chisel or the MOAKS tool. It's a relatively easy process, just don't use a sharp chisel as it will cut the metal on the key instead of displacing the metal onto the screws.

Very informative thread

I fixed this gun finally !! I took this gun apart several times thinking all the problems were in the upper. I finally took the a look at the lower. I started with the buffer and spring thinking the spring might be weak. There was no buffer or spring, the previous owner had changed the buffer and spring out with a hydraulic buffer replacement. This POS was causing the bolt to slow down to the point that all the gas was blowing out in places all over the gun. So there was not enough gas pressure to force the blot all the way back causing the bolt to stop before grabbing the next round. So after some major cleaning ! I took the buffer and spring out of my Rock River and the gun worked with not problems. Today we went to the gun show bought the new parts and problem solved. Thanks for all the help !

Holy crap thats funny !! Dont guess Ive ever seen that problem before !!

Glad yall figured it out !!

I'm sure you figured it out since the post is over a week old but from the picture the BCG does look somewhat dirty. Disassemble, clean then oil. That might fix the problem.

Ok, just saw the rest of the pages..duh.

That is a myth on the gas rings.