AR experts, please help diagnose...

[SURVIVOR619]

Had these problems today, out of about 200 rounds, 10 of them had this dented case when chambering.. The bolt jammed with the round angled into the ramp..? Is the bolt cycling too quickly? This problem began after about 150 non-issue shots... Another oddity was that the bolt would not stay open on some of the last shots, yet with the next magazine would..? Tried again with the erred magazine and it held open next time..?..?..

Thanks in advance for helping an AR goon.






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[repubconserv]

What ammo you got there?

[SURVIVOR619]

BTW, these are Lake City reloads if that matters..

I'm using a standard carbine buffer in a 16" carbine upper.


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[SURVIVOR619]

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[SURVIVOR619]

That shot above is of two successfully fired and ejected rounds... Checking to see if any oddities with extraction (random scratches on bottom of case)..


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[DarkSoul]

Did you reload the rounds? It looks like the rifle is short stroking, could be a few different things, could be ammo that's not hot enough, check your recipe (if you are reloading).

If it ran fine and as the day wore on it started to do this, possibly not enough lube on your rifle. Remember that ARs will run dirty, but they won't run dry.

[SFgiants105]

As per usual, my first impulse is to ask if you tried using different magazines. I have come to hate metal constructed AR mags; I prefer composite. Anyway, it seems that the bolt isn't grabbing the round properly, which in my mind is a bolt problem (face, not carrier group) or magazine problem. Try using different mags with the same ammo, and if it happens again, use your current mags with different ammo.

If it still occurs after that, I guess you could try playing around with other things. It could be the buffer spring, or the bolt, or the BCG, or maybe the barrel isn't lined up properly. I've never seen any malfunctions like that.

Let us know what it ends up being; I'd be interested to know.

[John Browning]

Try different mags and different ammo as a first fix. My bet is on crappy mags. If the mag doesn't sit up high enough, the bolt won't catch enough of the case head when cycling. You'd have to have REALLY crappy mags to be that out of whack, but they're out there. Does your upper have M4 cuts? What about the barrel? Pictures of the extension and upper receiver fit will help.

That ammo looks terrible, btw. I'd try something different.

[SURVIVOR619]

Yeah it is dirty brass... Shoots like a gem out of my AK... It could likely be a lube issue. I should've taken pics of the jams as they occurred.

I'm using magpul pmags from Midwest PX that are 20 rounders cut down to 10 and pinned...


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[SURVIVOR619]

Ok more pics.. Any other thoughts? Looks to me like upper mates just fine with lower.. Yes, M4 feed ramps. Excuse the dirty... Haven't given her a cleaning yet... Thanks again anyone who may be able to assist..

Lower






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[SURVIVOR619]

Lower with upper...



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[SURVIVOR619]

Ramps




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[SURVIVOR619]

Bolt and magazine...









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[Ruiner]

I'm going to say it's an issue with the magazines. This sometimes happens with the 20rd PMAGS when they are blocked. The follower gets bound and the rounds go up at a steep angle, causing the bolt to hit it at that exact spot. Try different mags if at all possible.

[SURVIVOR619]

I had 4 of these magazines in rotation...


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