I brought my new AR to the range today and put 69 rounds through it. 30 HSM 5.56 75gr, 12 BHBB 75gr, and 27 Guatemalan M193 surplus. The reason that I only shot 27 of the Guat instead of all 30 in the box is that three of them failed to feed. The tip of the bullet ended up pointing above the chamber, and the bolt ended up closing on the side of the brass case. I don’t find it easy to fault the ammo, since it’s been fine in my other rifles. This AR is a 14.5" w/carbine gas system, and an H-buffer. Brand new. Bought the upper and lower, each fully assembled. The gas key is staked, and solid. What appears to have happened is that after firing a round, the bolt, on returning to battery, is catching on top of the brass, just forward of the case head. I had it happen while using a used steel magazine, and also with a brand new Pmag. Can anyone help explain this one? See below.
Ok. Now that we know what we are dealing with you need to isolate the problem. I would use a different magazine and fire the Guat M193 by itself and see what happens.
What other AR’s have you fired this ammo in without problems?
It sounds as if it may be really hot ammo. Do you have any USGI aluminum magazines?
Were you using the same magazine for the entire outing, or did the 30 rounds of Guatemalan M193 have their own magazine?
My initial thought on this was a defective magazine. I got a TangoDown ARC magazine when they first came out, and had these types of failures about every five rounds with it.
I’d remove the magazine you used with the Guatemalan M193 from the equation and see what happens.
Folks he stated it happened with both a steel mag and a P mag. That being the case I agree that you should try some different ammo and see what happens. A total of 69 rounds is not telling you all of what you need to know.
Not saying you should expect nor accept such an issue with a BCM no matter how hot the rounds are, just dictating the logical next step.
Not seeing it, but even if it was crimped too hard it would not cause feeding issues.
OP just keep shooting the weapon, but try longer sessions with each type of ammo. That’s the best way to narrow down whether or not it is intolerant to that specific Guatemalan M193.
Hi folks, thanks for the input. I feel kind of stupid for leaving this fact out (I may have posted before taking the time to add two and two). But during that first shooting session, I had failures of the bolt to lock back after the last round in the mag. For whatever reason, I didn’t consider that two different malfunctions would be symptoms of the same problem. Now I’m fairly certain that this only happened with the Guat, but am not 100%. That’s why I’m going back out today with 100 rounds each of the BHBB, and the HSM, and 120 rounds of Guat. I will narrow this down. I really don’t think it’s the mags. It seems, now that I think about it, to be a classic short stroking problem, with the ‘bolt over’ being the symptom. If it happens even once, with ammo other than the Guat, I suppose it could indicate either gas leakage, or an out of spec gas port drilled in the barrel. We’ll see what happens.
Well, unfortunately the problem doesn’t seem to be the ammo. I had several more malfunctions. With the Guat, they were mostly failures to chamber a round. It wasn’t even bolt-overs this time, it was the bolt closing on an empty chamber, with rounds still in the inserted magazine. The top round in the magazine ended up looking like this:
Judging from the linear mark on top of the case, it doesn’t even look like the bolt travelled far enough back to clear the case lip. Unless I’m reading that mark the wrong way.
With the HSM and Black Hills ammo, there was no problem chambering any of them after firing one off, but I had failures of the bolt to lock back several times with three different magazines- all in good working condition (two of them brand new Pmags). Roughly 30% of the time, the bolt would not lock back with an empty mag.
So now, it looks like I’ll have to go through the proper channels to get this taken care of.
Look forward to seeing where this goes- this could potentially be the first I’ve heard of a BCM having a factory defect. I guess it had to happen eventually.
I had considered dropping in a standard carbine buffer just to see. Actually, my other 2 ARs are ‘builds’, both 16", with mid-length gas systems, and both have standard buffers. With the same ammo and with that same steel magazine, neither have had similar problems.
I figure that something is still wrong though, because an H-buffer should work fine with a 14.5" carbine. I wouldn’t be comfortable thinking that my carbine is the exception in a world where so many others successfully run the same system.
That’s a Knight’s M4 RAS, which I installed. Everything I’ve done since getting the gun has been of a bolt-on nature except for the installation of the MOE grip. Otherwise, the BCG, the upper, and the complete lower are as-received.
With three different known-functioning mags, I did the one round test several times. It locked back on most of them, and came back to battery on the empty mag around 30% of the time. Mostly with the year 2000 headstamped Guat M193, but also with the newer HSM 5.56 and the BHBB .223 .
