I've got a Patriot Ordnance 308 Edge SPR I'm developing loads for. An odd thing for me happened this afternoon. I began testing for this rifle with Sierra 180gr Pro Hunters on IMR 4895. Loads only 2/3 the way up the Hornady manual powder charge range was where I stopped at that time, and no pressure signs on the case or primer ever showed up, and Chronograph speeds were as expected.
Now, fast forward to today in July, about 25 degrees warmer outside (though I didn't let the rounds sit in the sun and get hot, they were cool to the touch upon loading into the rifle.) Same exact process followed, however today, every test load below, equal, and above those powder charge levels had a puckered firing pin divot show on the primer cups.
I thought this might be due to the 25 degree warmer temperature, so I put 5 rounds in a cooler on ice, waited for them to be very cold, loaded, fired, same result on the primer, a puckered or raised up ring right around the firing pin. The rest of the primer does not appear flattened, just that raised ridge around the firing pin dent.
Any good ideas as to what I'm doing that is giving me this different result? I'm out of ideas and a bit frustrated/stumped. This rifle appears to dislike loads toward max charge which seems pretty odd. It does have a 3 position gas block which I've triple ensured is set to the correct setting.
Brass is brand new Starline 308 brass. Primers are Winchester Large Rifle. IMR 4895 powder (again, only 2/3 the way up to maximum charge in Hornady manual. ((Lyman manual says to go even hotter)
Thanks.