AR 10 malfunction

[ARfiend]

I built a POF-USA lower with a dpms panther upper. I am having a couple of issues. Doesn't always load next round into the chamber and it accidentally bursted 4 or 5 times the last time I shot it. Any suggestions

[freonr22]

a 2rd burst? or more than that?

[ARfiend]

mostyly 2 rnd bursts but there might have been a couple 3 rnd in there

[kiralc]

sounds partly familiar

Part of your problem sounds very familiar...

I've been struggling with failures to cycle out of my 20" DPMS .308. They seem to be somewhat ammo dependent and very mag dependent. I have various DPMS .308 models and they do not have the same quirks. Each seems to have more or less tolerance for different types of ammo. In the case of the TAC-20, it simply refuses to cycle using 1968 DAG M80 - regardless of the mag. However, it will cycle other M80 surplus as long as I use a Magpul mag. My TAC-20 won't cycle M80 (even brand new Federal) if I use the DPMS or C Products magazines. This is probably part of why they recommend only the heavier rounds. Of course, this only addresses half of your problem, but...

All of my DPMS lowers have Rock River 2-stage triggers. If I had to guess, you probably have some slam fire action going on - but I'm only guessing that it may be your hammer riding the pin down. I've also heard that an overly-long pin or badly manufactured bolt could contribute to slam fires - both of which should be verified by the factory (ie. you should consider returning the upper or at least having a gunsmith check it out before your upper detonates 6 inches from your face).

Erik

ps: what ammo/mag combo do you use?

[ARfiend]

I am using dpms magazines with 150 grain federal ammo.

[kiralc]

yup... familiar

I am using dpms magazines with 150 grain federal ammo.

That sounds about right. The slam fires (if that's what they are) are new to me, but the DPMS .308's do seem to struggle with the lighter rounds. If you poke around on DPMS's website and user forums, you'll find that they stress the need for 168 gr (and higher) bullets in order to have reliable cycling. I'm still playing with ammo/mag combos to see what each upper can tolerate and yours will have its own quirks. However, before you start exploring the miriad of ammo/mag combos, I'll share the following...

I once had a Charter Arms AR-7 (it's a .22 lr) that would have anywhere between 2 and 8 round bursts. Which I thought was loads of fun until one of the rounds went off before being fully seated in the chamber. Since it was an aluminum upper, the premature detonation caused the side of it to blow out. Luckily, since it was only a .22, I escaped injury - but I shudder to think what would have happened if I had been playing that game with a hunting round... be careful.

E

[ARfiend]

Thank you all for your help on this issue, I tried the different grain ammo and that unfortunately did not help out. But, I swapped the trigger, hammer and connector out from a spare parts kit and the rifle now works perfectly. So if anyone has similar issues and the ammo change did not do anything try out the trigger swap.