BCG Issues

[SactoPlinker]

UPDATE!!: Problem solved, embarrassed to say but I screwed the receiver extension in one turn to far. So I backed it out one turn and voila! Bolt locks back properly. thank you all for the help though, much appreciated!
Hi all!

Don't worry I searched and I think I have isolated the issue but before I go about trying to fix it, I wanted to see what the experts thought.

Some background:

The AR was just built (heres the link to the thread: http://www.calguns.net/calgunforum/s...d.php?t=575219) and I took it to the range on Thursday. Fired the first round no problem, except it didn't feed the 2nd round and continued to have to pull the charging handle to load each round for about 40 shots. In that period sometimes the it didn't eject the case at all or would only pull the brass out about halfway (Still stuck in the chamber a bit). The ammo used was PMC Bronze .223 by the way.

Switched mags and added lube all throughout this. After about the third box it started to cycle consistently and was very accurate. Still had a some failures to ejects and would have to clear it. What I noticed is the BCG won't lock back all the way, it catches on the carrier as opposed to the bolt lugs. When you pull the charging handle back all the way, it is not enough to get the bolt catch in front of the lugs.

So is it short stroking? Shorter spring fix the issue? Any advice is greatly appreciated.

Buffer Spring length: 11 inches
Buffer Weight: 3 oz.

[neal0124]

Without looking at it in person I'd have to say you have some kind of mechanical interference going on. The wrong buffer with the wrong tube or an incorrect spring. The carrier needs to come back about 1/4" past the bolt catch.

Remove the spring, re-assemble the rifle, then pull the charging handle back until the buffer bottoms out in the buffer tube. It should clear the bolt catch, if it does then you might have been using the incorrect spring. If it doesn't clear the bolt catch then you may be using an incorrect buffer.

[Josh3239]

Sounds an aweful lot like short stroking, it doesn't help you are using weak PMC. Get full power 5.56mm. If it cycled fine for a few shots it likely isn't your rifle otherwise it wouldn't have cycled fine at all. When it was cycling right did it lock the bolt back correctly? Place an empty mag in and pull the charging handle to the rear, if it locks it 99% of the time isn't the rifle nor mag. Like I said, probably short stroking and you should stick to full power 5.56mm, at the very least break it in with the more powerful ammo.

[neal0124]

I've shot several thousand rounds of PMC bronze out of an 18" barrel with a rifle length gas system, and do not believe it is weak at all. Wolf or Tula on the other hand absolutely is weak and causes short stroking on longer gas systems. The original poster stated that when the charging handle is pulled back all the way it doesn't clear the bolt catch. That implies to me that there is a mechanical blockage if during a manual cycling of the action it doesn't travel to it's rearmost point.

[Josh3239]

The original poster stated that when the charging handle is pulled back all the way it doesn't clear the bolt catch. That implies to me that there is a mechanical blockage if during a manual cycling of the action it doesn't travel to it's rearmost point.

I see, must have missed that. The OP then needs to give us more info; extention tube, spring, buffer, and maybe details about the upper. Suppose something could have been out of spec.

I've shot several thousand rounds of PMC bronze out of an 18" barrel with a rifle length gas system, and do not believe it is weak at all. Wolf or Tula on the other hand absolutely is weak and causes short stroking on longer gas systems.

Irrelevant. The OP isn't shooting your 18'' barreled rifle length gas system and chances are anyways he is shooting a 16'' carbine or midlength but he didn't specify. Either way it is as irrelevant as my rig and the ammo I use.

It is just a fact that PMC is weak. It is mass produced factory so it isn't that consistent but in general the stuff is not loaded as hot as "real" 5.56mm and there is no shortage of reports of low muzzle velocitys when chrono'd.

[SactoPlinker]

The stock is a Magpul MOE with a mil-spec extension, I think most of that was lined to the thread I attached but for ease of reference I'll list it here.

The Upper is a Stag Model 3 with a Rock River M16 BCG, it has M4 feedramps. As far as buffer and spring go, I don't know what brand they are, a vendor at a gunshow included them for 5 bucks extra.

I agree on the ammo, the PMC was all I had access to at the time (my bolt action savage is chambered in .223) but I'm really thinking the spring is too long because even when you manually pull the charging handle back all the way, it will not clear the bolt catch.

[neal0124]

He is shooting a 16" carbine. With a gas system that short on an barrel of that length he has a much longer dwell time than an 18" with a rifle length system or a 16" and a mid length system. That would allow more time for gas to act against the bcg to cycle it, so even weak ammo will have an easier time pushing the bcg rearward. PMC bronze is a .223 loading so it isn't going to be loaded as hot as "real" 5.56 anyways. All these ammo's are mass produced in a factory so the chances of inconsistency are always going to be there. Regardless, PMC bronze would have plenty of power to cycle a rifle. The OP is using a magpul moe stock. I've seen others that have had a similar problem when using an A2 stock. The problem was that they used a screw that was too long, it protruded into the buffer tube and the buffer was being stopped short. I think there is some interference going on and not allowing the carrier to cycle fully, and with a setup like his the only thing I can think of is that the spring is too long and the coils are stacking up upon compression and stopping the carrier short.

[neal0124]

The stock is a Magpul MOE with a mil-spec extension, I think most of that was lined to the thread I attached but for ease of reference I'll list it here.

The Upper is a Stag Model 3 with a Rock River M16 BCG, it has M4 feedramps. As far as buffer and spring go, I don't know what brand they are, a vendor at a gunshow included them for 5 bucks extra.

I agree on the ammo, the PMC was all I had access to at the time (my bolt action savage is chambered in .223) but I'm really thinking the spring is too long because even when you manually pull the charging handle back all the way, it will not clear the bolt catch.

Take the spring out, reassemble the rifle, then manually cycle it. If it clears the bolt catch then the problem is the spring. If it still stops short then there is another problem going on.

[SactoPlinker]

I'll go do that now haha

[SactoPlinker]

Nope, still wont clear by literally a hair.