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#6351884 - 06/29/16 02:32 PM AR-10 Blowing Primers
LFD2037 Online   happy
THF Trophy Hunter

Registered: 11/05/08
Posts: 6314
Loc: TEXAS
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???

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#6351892 - 06/29/16 02:36 PM Re: AR-10 Blowing Primers [Re: LFD2037]
LFD2037 Online   happy
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Registered: 11/05/08
Posts: 6314
Loc: TEXAS
Brass was ejecting @ about 4 o'clock position.
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#6351903 - 06/29/16 02:47 PM Re: AR-10 Blowing Primers [Re: LFD2037]
ChadTRG42 Offline
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Registered: 09/16/09
Posts: 9397
Loc: Lewisville, TX
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.
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#6351915 - 06/29/16 02:55 PM Re: AR-10 Blowing Primers [Re: LFD2037]
Pig_Popper Online   content
Tracker

Registered: 08/16/15
Posts: 571
Loc: Fort Worth
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
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#6351929 - 06/29/16 03:05 PM Re: AR-10 Blowing Primers [Re: ChadTRG42]
LFD2037 Online   happy
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Registered: 11/05/08
Posts: 6314
Loc: TEXAS
Originally Posted By: ChadTRG42
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.

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!
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#6351957 - 06/29/16 03:24 PM Re: AR-10 Blowing Primers [Re: LFD2037]
Pig_Popper Online   content
Tracker

Registered: 08/16/15
Posts: 571
Loc: Fort Worth
How did it shoot with the OEM gas block?
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#6351961 - 06/29/16 03:27 PM Re: AR-10 Blowing Primers [Re: LFD2037]
ChadTRG42 Offline
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Registered: 09/16/09
Posts: 9397
Loc: Lewisville, TX
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.
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#6352049 - 06/29/16 04:05 PM Re: AR-10 Blowing Primers [Re: LFD2037]
ChadTRG42 Offline
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Registered: 09/16/09
Posts: 9397
Loc: Lewisville, TX
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.
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#6352109 - 06/29/16 04:47 PM Re: AR-10 Blowing Primers [Re: Pig_Popper]
LFD2037 Online   happy
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Registered: 11/05/08
Posts: 6314
Loc: TEXAS
Originally Posted By: Pig_Popper
How did it shoot with the OEM gas block?

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.
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#6352115 - 06/29/16 04:54 PM Re: AR-10 Blowing Primers [Re: ChadTRG42]
LFD2037 Online   happy
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Registered: 11/05/08
Posts: 6314
Loc: TEXAS
Originally Posted By: ChadTRG42
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.

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! hammer

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).
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R.I.P. CPO Matt Mills-(DEVGRU)- You will NEVER be forgotten!
10-25-75 / 8-6-11 *K.I.A.*

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#6352155 - 06/29/16 05:16 PM Re: AR-10 Blowing Primers [Re: LFD2037]
LFD2037 Online   happy
THF Trophy Hunter

Registered: 11/05/08
Posts: 6314
Loc: TEXAS
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.
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R.I.P. CPO Matt Mills-(DEVGRU)- You will NEVER be forgotten!
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#6352177 - 06/29/16 05:26 PM Re: AR-10 Blowing Primers [Re: LFD2037]
JCB Offline
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Registered: 02/06/07
Posts: 22835
Loc: M.I.A.
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.
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#6352259 - 06/29/16 06:39 PM Re: AR-10 Blowing Primers [Re: LFD2037]
jeepercreeper Online   content
Extreme Tracker

Registered: 11/07/10
Posts: 3639
Loc: DFW
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.

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#6352268 - 06/29/16 06:49 PM Re: AR-10 Blowing Primers [Re: LFD2037]
ChadTRG42 Offline
THF Trophy Hunter

Registered: 09/16/09
Posts: 9397
Loc: Lewisville, TX
Originally Posted By: LFD2037
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.


Yes, this is the primer debris left over from the blown primers.
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#6352272 - 06/29/16 06:55 PM Re: AR-10 Blowing Primers [Re: LFD2037]
ChadTRG42 Offline
THF Trophy Hunter

Registered: 09/16/09
Posts: 9397
Loc: Lewisville, TX
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!!)

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