Need some ideas on what may have caused this problem. The details are a little fuzzy because I didn’t have time to stop and pay attention to what was going on during this course of fire.
What happened was I fired a round, the case extracted and then the bolt got hung up. I tapped the mag and the bolt closed and fed a round. Fired, same thing happened again. Tapped the mag, bolt closed and fed a round and then no further issues for the rest of the day. This was on my third mag or so. Shot probably 150 rounds or so that day, so it happened pretty much square in the middle of the session.
So that almost sounds like it was short stroking (ammo? no reason to suspect the gas system yet, it has been solid so far) but it still managed to feed a round. I suppose the mag might not have been seated, but twice? It was an old USGI mag.
Just trying to understand what may have been going on.
Fuzzy is an understatement…
What gun, what config, what ammo? How was it “hung up”? Did it go into battery upon tapping the mag? Did you note which mag this was?
Not trying to be an ass but it’s hard enough trying to analyze things over the net. It makes it next impossible without more details.
Can’t confirm on the ammo, I had two or three different types loaded. Most was 55gr but there were a few heavier rounds as well.
For the config it is a Rainier Arms match 16" barrel and gas block, BCM BCG, mid length gas system with a H buffer, standard spring. And yes, tapping the mag did cause it to go into battery and successfully feed the round. So the BCG made it far enough back to eject the spend case, and started to feed the next and got bound up at that point. Not sure how full the mag was at this point.
From the details given, I would say it was the magazine. I have had a few hangups like that using D&H mags (all 3 where bought together and all three had the same problem… never had any problems with other D&Hs ???).
Probably the mag spring, follower tilting and your feed lips might be sharp or distorted. As others mentioned hard to diagnose over the internet. Replace the mag if in question
Had this happen on Pops Colt. We unwrapped a new (in the 60’s or 70’s probably) mag and everything went back to normal. It could still be another problem but I would have tried a new mag right then.
It could be a combination of things. Aluminum magazines have more drag on the round being fed than Magpul mags do. More force is required for reliable feeding with aluminum mags. I can run a heavier buffer (without changing the action spring) on my carbine with Magpul mags.
It could be that your BCG was getting a bit dry. With aluminum mags, I find I have to oil up my BCG more often (this is using gun oil, like Birchwood Casey’s Gun Oil or Rem Oil. Just recently started using Froglube so we’ll see how that pans out).
It could be your action spring is getting worn. I suspect that’s what’s happening with my carbine. It’s just a standard spring and probably is just beginning to sack, leading to the occasional failure to feed with aluminum mags. Same thing could be happening with your AR.
I may be wrong, but I don’t see how a weak mag spring would cause the round to be partially stripped from the mag like this. A weak mag spring should cause bolt overs, rounds to nose dive or to get crossed up
The action spring shouldn’t be worn yet as the gun has less than 500 rounds through it so far. I wonder if a stiffer action spring may have helped in this case however? I guess assuming it wasn’t weak ammo
Ok, since people keep asking, here is the full build:
Lower: PSA receiver and parts kit.
ALG ACT trigger
mil spec 7074 tube, standard carbine action spring with H buffer
Magpul CTR stock
MOE+ grip
Upper: VLTOR MUR upper receiver
Rainier Arms Match barrel, 16", mid length gas system. Rainier Arms gas block, pinned by RA
Apex Handguard
Smith Vortex flash hider
BCM BCG
T1 micro with magpul BUIS
Any other details I am missing?
The mag in question was an older USGI with a magpul follower. It might have even had its spring replaced recently but I’m not 100% if I did that or not. I thought I put new springs in all my USGI mags when I put the magpul followers in them.
So the three culprits I am hearing are a weak action spring, under powered ammo or somehow out of spec mag yes?
I suppose we could throw a gas leak in there too but I really don’t think there is enough evidence to suspect that yet.
ETA: It has run fine with pmags so far. And the rifle was clean with lube visible on the BCG at the beginning of the day FWIW
It’s a PSA action spring from their parts kit? I’d replace that with a BCM or Colt replacement first, they are cheap.
If it were a gas leak or weak ammo it wouldn’t cycle rearward completely and might not strip the round from the magazine to chamber.
The action spring pushes the action into battery. It should be able to overcome the magazines hold on a round to feed and chamber and overcome any friction the magazine may offer unless the magazine is VERY out of spec or the gun is dry and dirty.
If it happened a few times on one occasion then I’d replace the action spring, throw the mag(doubtful that it’s the problem), lube it good and run it again.