New DPMS G II AR .308. Before shooting I swapped out the factory gas block w/an adj. gas block. Due to not being able to adjust the gas block w/out removing the HG, I set it in the middle. Fired one round to make sure BCG locked back, it did. Loaded a mag of 20, no firing issues. Loaded a couple more mags & kept having FTfeed, failure to pick up next round in mag, failure to go into battery, BCG getting jammed forward & taking gorilla strength to pull it back (even though the next round hadn't even loaded). Decide to pick up the brass & notice some primers look fine, some have a hole in them w/a piece of gun powder lodged in the hole & some primers MIA. Magtech 'M80' cheap plinking ammo is the only ammo I tried. Was scared to try anything else after I found these issues. BCG got pretty dirty pretty fast & wasn't oiled very much from this drying it quickly. WTF is the problem here???

Brass was ejecting @ about 4 o'clock position.

First, you are getting excessive pressure signs. Is the ammo too hot, not sure? A lot depends on how much pressure is coming back at the bolt. If you have the new gas block over gassed where too much gas is coming back, it can cause pressure issues. Since it is a new gas block, my guess is this is the issue. I would dial the gas block where as little gas is coming back as possible, and adjust it more open a little at a time until you find the right setting. Also you need to make sure the gas ports are properly lined up and you are not getting any gas bleeding out. I have had this issue once on an AR in 223.

Close the gas port all the way and shoot 3 rounds - inspect the brass and primers , if all good work half a screw turn at a time out (more gas) until the bolt locks back on empty. Adjust out an additional half turn for good measure and lock in your setting.

It'll be easier to do all this with no handgaurd installed.

If you plan to shoot a bunch of different ammo types and tune to each then a different handgaurd that gives you access to the adjustment screw is recommended.

Good luck

If it was over-gassed, would EVERY case land pretty dead-on @ 4 o'clock, like it's under-gassed? Also, it's not locking back after last round, like it's under-gassed. Still leaning towards over-gas issue? Thanks!

How did it shoot with the OEM gas block?

Yes, you can easily be over gassed and it not lock back. Same thing happens with a pistol when you shoot too hot of a round. The slide or bolt comes back so hard that it doesn't lock back.

But, you are blowing primers on a crimped in primer, which I will say takes talent to do so!! That's a lot of pressure at the bolt! The round in the middle has the anvil protruding from the center of the primer.

Idiotically, I never tried it w/the factory GB. I'd read so much about how all factory AR-10's, especially the DPMS G II's, were over gassed from the factory so I thought I'd take out that issue from the get-go.

Sorry for my ignorance, but the "anvil protruding" & "blowing primers on a crimped in primer", leads more or less towards the gun being over gassed? FYI: I thought that was a grain of powder protruding the the primer!

If all this is leaning towards a gas block issue, then I may just order an adj. gas block that I can adjust w/the HG in place instead of the cheap one I ordered (where I have to remove HG, loosen GB mounting screws, slide GB back to reach the set screw for the 'adjustment' screw, adj. Then put it all back).

Breaking down the BCG. When I removed the firing pin all this primer trash fell out. Firing pin was very difficult to remove, covered in black soot and cotter pin that holds it in is slightly bent.

In my opinion you have two issues here and one may or may not be related to the other.

First off the blown primers is a obvious pressure issue. Could be caused by several things including bullets being seated to deep, really tight chamber, or really hot loads.

The other issue with the feeding, failing to pick up another round, etc is most likely a gas issue. The failing to feed, pick up a new round, and locking up tight kind of gives mixed signals though. Could be over gassed or could be under gassed. I think this has little or nothing to do with your blown primers though. If you were waaaay over gassed I think you would be having extraction issues due to bolt trying to cycle to early causing rims to be ripped and failure to extract from chamber.

If it were my gun I would treat these as two separate issues starting with trying to find out why the primers are blown first. That's the dangerous part of this equation.

I would simply put the factory gas block back on and shoot it with a couple different types of ammo. If it still has issues....send it to DPMS.

Yes, this is the primer debris left over from the blown primers.

You can see the anvil in the pictures below of the primer. (The rounds you are shooting have a crimped in primer. The crimp is so that the primer does not come out of the brass case on a hot load. You have enough pressure to blow primers even with a crimped in primer. So, that's a lot of pressure!!)

I have 5 different types 7.62 ammo. I'm going to go thru the GB adj. process & shoot quality ammo. If I get it dialed in then I'll try all the different ammo I have & see what the results are. I'll know if it only does it w/the ammo that did the above crap, then I'll know that ammo has an issue (just bought 500rds of it ). Next time I go to the range I'll do this but what if:

I get the BCG to lock back w/just enough gas (proper gas amount), & it still does this w/other ammo, what should I do next? Thanks for all the help!

Have you tried chambering a round and then unchambering the round without firing it to see if the bullet is pushed back in case?

Ammo is the problem.

Find a load that shoots well, and safe, then adjust the gas block to operate properly.

When I developed the load for my rifle (we as yours), I found a load that shot well, and did not hurt the brass, but it was ejecting at 1 o'clock. After the load was found, I switched to an adjustable block, turned it down all the way, would not rechamber a new round, then opened it up until it ejected at 3 o'clock. Lots of oil, and it has been fine ever since.

Just did. No difference in bullet depth.

I wouldn't be so sure it's only an ammo problem. My last DPMS Recon would not chamber any round due to the overly tight chamber. DMPS .308's (IMO) are infamous for tight chambers. I'd be very curious if the OP would do as A2B said if he'd notice that the bullet isn't pushed back into the case.

I can only speak for myself but after my last Recon (a brand new gun that had obviously never been test fired at the factory, because it wouldn't even chamber ANYTHING I put in it) - I won't own one again. I had previously owned several DPMS .308's with no issue but that one admittedly soured me on them. Besides, once Armalite came out with the DEF10 for the same money, the decision will always be to go that route.

I see the OP replied and saw no difference in bullet depth. I'd still have the chamber checked if it was mine.

What was the reason for swapping the gas block in the first place? I learned my lesson about replacing parts before shooting a gun as is. Never again.

I have run into this issue before and found the first blown primer came apart like yours did, then the problems snowballed from there until I cleaned all the parts on the gun. I found all kinds of pieces like you are doing. Once I cleaned the gun and double checked everything on assembly, the action worked properly.

A lot of problems can be created by the gas block. Leave the hand guard off to dial the gas block in if possible.

Because everybody says they're over gassed from the factory so I was trying to get a jump on improving it. Believe me, I'll never alter a gun before I make sure it function properly again!!!

I believe this is what happened w/all the FTFeed/FTE/etc. The firing pin was jammed pretty damn good due to all that primer trash. I literally had to get a screwdriver & pry the firing pin out of the BCG. The BCG was dried out from all the gas/heat going back into it. The powder residue on it was slightly charred & this was <40 rds. It was filthy.

[Magtech 'M80' cheap plinking ammo is the only ammo I tried. ]


This is going to be your primary problem. The blown primers are because this load is too hot for your rifle. You usually see this with suppressed AR-10's with factory gas blocks. You don't mention being suppressed so an adjustable gas block will not create more gas than what the loaded round creates. However, a load too hot obviously creates more gas. Your case heads and primers indicate the ammo is way too hot for the rifle.

I would try some different ammo. Or maybe contact Magtech to see if they had a bad lot.