I don't venture outside of the GAHTF...at all, but I thought I'd pick y'alls brains on this one.  I can't figure it out.

DPMS LR-308 with Fulton Armory 18.5" barrel

SLR Adjustable gas block

SilencerCo Specwar Muzzle Brake

SilencerCo Specwar 762 Suppressor

Load data: 43.5gr Varget, LC brass FL resized, 175gr SMK, WLR primer.  Chrono'd right at 2600fps.

I worked this load up using the suppressor and found where the gas block needed to be adjusted to for the rifle to not beat up the brass terribly bad but still have positive ejection.  I've fired probably 200-300 rounds using this combo with no ill effects.  No ejector swipe, no flattened primers, everything running great.

I took the suppressor off yesterday to find out how much more gas the rifle needed to run in the event I wasn't using the suppressor and to find out where the unsuppressed zero was.  I opened the gas block up by 1 click, expecting that not to work, but it was a good place to start.  Cartridge fires, but only partially ejects.  Pull the case out of the ejection port and it has a pierced primer.  Wierd.  Open the gas block up two more clicks and the rifle ejects, but without much authority and the primer is *almost* pierced.  Open the gas block up one more position and ejection is good, but the primer is pierced (again).  At this point I turned the gas block back to where it ran well suppressed and put the suppressor back on.  Misfire.  Take gun apart and find piece of primer stuck in firing pin channel and learn that firing pin is mildly eroded...not surprised.  Clear the shit out of the bolt and try it again.  Despite a mildly eroded firing pin, everything is back to normal.

First of all, I intend to replace the firing pin.  But, why is the rifle piercing primers when NOT suppressed, but everything is fine with the suppressor on it?  Shouldn't it be the other way around?

I would guess once you replace the pin it should work fine with suppressor on or off. I have almost the same setup but mine is a Gen II Hunter with 18.5 barrel, using a Saker 7.62. I also have a LR308 rebarreled in .260 Rem, a match rifle.

I would recommend not using Winchester primers in a gas gun. Some years ago they did away with the plating on the primer cups and made them more susceptible to piercing. I was shooting a lot of Highpower matches with a 20" match A2 service rifle, and began getting pierced primers a lot after I got some WIn primers in the new blue packaging, and they were not nickel plated. Every time this happened I had to replace the firing pin. Other highpower shooters I know noticed the same thing. Of course we were shooting pretty stiff loads with Sierra 77 and 80 match kings, but within SAMMI spec. I switched to CCI BR4s for 600 yards and CCI 41s for short line - no more piercing. I also like the Wolf small rifle magnum primer.

In my .308 gas guns I am using Federal Gold Match large rifle or Wolf Large Rifle primers. When the Wolf primers came out they tested even better on the chrono, and they are pretty thick; it seems they are just a tad fatter and fit tighter - good for one last load when the primer pockets get a little loose.