Need help with failure to feed

[Edvil91]

Fellas,

I need help with a failure to feed issue. The rifle was having these issues almost every other round. Im not sure if it's the mag or something else. The mag used was a 308 pmag. As you'll see in the photos, the mag has some damage from usage - only 50 rounds were shot, both through the rifle and mag. About the rifle, it's a armalite ar10B upper that was converted to a "A" version upper to accept pmags (done by Randall - thanks!). On a side note, I need to replace the mag catch spring because I did experience seating issues...hopefully that was not the reason for all this?

Anyways, here are some photos. Any help would be greatly appreciated. Thanks your time!

[buellster]

Looks like the bolt is over-riding the rounds. My guess would be a mag or mag height (the distance the rounds protrude into the upper) problem.

[Edvil91]

Looks like the bolt is over-riding the rounds. My guess would be a mag or mag height (the distance the rounds protrude into the upper) problem.

hmm... You think that may be because I'm using an ar15 magcatch rather than the ar10 one? I did this because of the bullet button I'm using. I did notice that they're a bit different.

[buellster]

I think the only difference in the mag catches is the length of the post. If it holds it firmly then it shouldn't be a problem. I would try a different mag type before I tried anything else.

[6mmintl]

Might help to take apart mag if metal and deburr/polish all wear surfaces, check for bent feed lips and lightly lube.

[kcstott]

P mags are plastic or polymer as all the mall ninjas say.

[phrogg111]

P mags are plastic or polymer as all the mall ninjas say.

Or, you know, scientists who developed the polymer... because polymer and plastic are synonyms... polymers are plastics, plastics are polymers...

[cdb2468]

if it has anything to do with the bolt or bolt carrier group it is being affected by gas. Make sure your bolt carrier gas thing on the top is staked in good and isnt loose, check for obvious things that would slow the bolt carrier down or leak gasses.. i doubt its being undergassed, but possibly... its not overgassed unless the cases are being extracted too soon and are grabbing onto the chamber walls much more than usual, robbing energy from cycling. look for signs of high pressure, brass shavings on bolt face, if the extractor is cutting into the metal as the bolt rotates and tries to extract the round, if there is anything unusual with the primer going on...

stretch ur mag spring?as the gun recoils the rounds in the magazine have a tendency to move forward as they have inertia, it could account for some or all of the forward movement, however i think thats unlikely, what i see is the magazine isnt pushing the next round up fast enough for the bolt to catch it... try a different magazine, call me crazy but if that doesnt work try different ammo... you'd be surprised on that one.... Im a gunsmith by trade, ive seen this a few times its ALWAYS a pain in the butt to solve these kinds of things... good luck!