Gunsmithing: AR failures at the range

[Beowulf]

I took my AR to the Applied Ballistics range today to sight in my new Eotech 512. I started having failures almost immediately (I took it out to the range two weeks ago and it was running like a champ).

My AR is a DPMS complete lower (I didn't put any parts into it) and a Palmetto State Armory upper that I just bought. I kept the BCG from old AR upper and I have no idea where it came from.

So, first mag in, I started having failures to fire. I was shooting Tula .223. Initially I just blamed the ammo. But as I proceeded through the mag, the primer strikes started looking lighter and lighter on the rounds that wouldn't fire. Then, I had it start periodically double firing on me (while still having periodic failures to fire and some rounds still firing normally).

I stopped shooting after that. When I got home, I pulled the upper and removed the BCG. That's honestly as far apart as I really feel comfortable taking it, while being confident I can put it back together (yeah, pretty pathetic, I know).

One thing I noticed, the firing pin seems to float freely in the bolt. By that I mean I can push it in, so the pin protrudes out of the bolt face, but then it just drops back loosely. I would have thought there would be a spring in there somewhere, keeping the firing pin tautly back, leaving the hammer to slam it forward. But I don't have another AR on hand to compare it to.

Anyone have any thoughts?

 

[NathanJefferson]

First the Firing pin is supposed to float freely. So that is ok.

Other than that someone will be along shortly with a few recommendations on what to check. I have heard that Tula is notorious for having hard primers, so maybe you hammer spring is a little weak? Were you using different ammo when it ran like a champ?

 

[mvician]

Firing pin = normal

Is the lower a factory build or did you buy it from someone who put it together?

Are you using the same ammo as you did when it was running like a "champ"?

Sounds like a problem in the fire control group which leads back to who built the lower.

 

[Beowulf]

Nope, same exact Tula on both trips. Same batch and everything.

I also took all the rounds that failed to fire and put them through my FN FS2000 and they all fired normally. I then put 4 more magazines worth through the FS2000 with not a single failure.

The lower was a factory DPMS lower I bought complete at the 1500 last year.

 

[1911ly]

I steer clear of steel case ammo. I have had to beat out the casings on about every third time. Some uppers might handle it better then mine. Have you ever deassembled the BCG to clean it? Double firing sounds like the firing pin is sticking. Maybe bent? The piston sticking? Taking the BCG apart is not as scary as it sounds. There are no springs to fly out. there are a bunch of Youtube videos on how to do it. I am thinking the issue is in the BCG. Any AR15 geru's out there?

 

[churchmouse]

No Guru but I have to agree that if you have never been into the BCG it could be build up or any related issue. It is only a cotter style pin and a few bits. Make sure it is totally clean and be careful of the seal rings when you re-assemble it.

 

[Mosinowner]

Hammer spring on wrong?

 

[jeremy]

Clean the BCG...

 

[sloughfoot]

Hammer spring on wrong?

This is the first thing to check.

 

[Beowulf]

Hammer spring on wrong?

Is this something that could cause a failure much later? I bought the lower a while back and probably had at least 500 rounds through it on my old upper. I had maybe 120 rounds through the new upper before I had this failure.

 

[jeremy]

This is the first thing to check.

It worked fine for its first year...

Highly, doubt this is the problem. OP, disassemble and clean the BCG...

 

[HamsterStyle]

As somebody that just finished his first build, I'll chip in my 2 cents. It is extremely easy to disassemble and reassemble the BCG. Give that a whirl and clean it up real good.

 

[Beowulf]

As somebody that just finished his first build, I'll chip in my 2 cents. It is extremely easy to disassemble and reassemble the BCG. Give that a whirl and clean it up real good.

Okay, the BCG does seem to be the general consensus. I'll see about getting it apart and clean it up next chance I get. The only bad thing is that I won't have any chance to hit the range again for at least a couple of weeks.

I'll try to remember to report back on my results.

 

[Shollz]

yeah, those bolts get way dirtier than you would think

 

[1911ly]

Okay, the BCG does seem to be the general consensus. I'll see about getting it apart and clean it up next chance I get. The only bad thing is that I won't have any chance to hit the range again for at least a couple of weeks.

I'll try to remember to report back on my results.

Please let us know! I think once you get it apart you will fine it is not as hard as you think. The easiest mistake to make is turning the piston/extractor 180 degrees. Take a few pics as you go for reference. You'll do fine. post if you need any help and youtube has a lot of videos.

 

[sloughfoot]

So, you guys think the bolt is not going fully into battery? That is the only way to get light primer stirkes after all. If that is your conclusion, scrubbing the barrel extension is also called for because cleaning the BCG certainly will not clean all those lugs in the barrel extension.

Everything works together in the AR. Since it costs nothing to look into the lower receiver at the hammer spring, I hope the OP does that too in addition to the thorough cleaning of the BCG and the chamber and barrel extension lugs.

 

[spyder]

Are you sure the lower is a stock, and no one ever worked on the lower? If you're doubling, there is something wrong with your disconnect, or, your sears don't have enough engagement. The double firing is in your control group. It is usually a problem with someone doing sear work. A lot of people don't know that the hammer and trigger sears are hardened. So when you do work on them, you take the hardening off... Later down the road, your edges that need to be crisp, are now rounded just enough to give you problems. Do a check for me. Make sure your gun is unloaded, take the mag out, cock the hammer (pull the charging handle back and then let the bolt go forward), and hold the gun above a very rigid surface (floor, counter) about a foot high, and drop the gun onto the buttstock. This will not hurt the gun in any way. If the trigger goes off, you have problems. Test two. Hold the trigger down (pull the trigger and keep it pulled), and then while keeping it pulled, pull the bolt back and let it go back into battery (mag has to be out to do this). Then, let go of the trigger (do this a few times). If the hammer falls at all, you have problems. Third test to check the bolt lock up... Take the BCG out ouf the rifle and extend the bolt all the way out (it twists out of the carrier toward the front of the gun), and set the BCG on its face on a table. If the carrier falls down onto the bolt, you have issues. Anyway, there are a few tests, try them.

 

[jeremy]

So, you guys think the bolt is not going fully into battery? That is the only way to get light primer stirkes after all. If that is your conclusion, scrubbing the barrel extension is also called for because cleaning the BCG certainly will not clean all those lugs in the barrel extension.

Everything works together in the AR. Since it costs nothing to look into the lower receiver at the hammer spring, I hope the OP does that too in addition to the thorough cleaning of the BCG and the chamber and barrel extension lugs.

Actually, I don't think that.

I'll but once the BCG is disassembled, there will be foud a significant amount of carbon, and fouling on the firing pin...

 

[karoozin]

That was my first thought. But I do agree the Tula is notorious for having hard primers.

 

[Electronrider]

I agree 100 percent with spyder. If your firing pin is free floating, then the problem is in your lower parts kit. I just went through a multiple firing problem and thought that I had a problem with my bolt carrier. Luckily I had another carrier and swaped it out. Still had the same problem. I then replaced my cmmg 2 stage trigger and have not had a problem since.