Reading Pressure Signs in a Semi-Auto

[Potss]

I just started reloading for my AR10, and I'm having trouble identifying press. This is because on this particular AR10, basically all factory loads, book minimum handloads, and even some milsurp are showing slightly cratered primers (but still rounded not flat) and ejector shadow/raised marks. No ejector smudge or smear, just the marks (some of which are raised enough to catch my nail slightly). Obviously none of this ammo is actually overpressure (in fact some of the min handloads won't even cycle the AR fully, but still have ejector marks). I believe these "pressure signs" are showing up because it is cycling a little fast and is suppressed.

So my question is, what other signs can I look for what working up to a max that will reliably show I'm approaching the max load for this rifle?

 

[Huskydriver]

First 2 questions ..are you shooting 308 or 6.5 and if 6.5 are you using a sfp bolt group?

 

[Potss]

Sorry, you are right should have clarified. .308 in a 20in barrel. Standard BCG.

 

[Huskydriver]

Could be dwell time related but honestly sounds pretty normal for a 308 without seeing pics. What length gas system are you running and I assume you have an agb?

 

[Sniper266]

Not an expert but just my 2 cents. When i did load development for my 6.5 creedmoor ar i went up in power charge by .3 incriments checking each case for pressure signs on the primer. The first real pressure sign i got was a blown primer. Not exactly when you want to find out, but after that I immediately stopped and knew the limits of the rifle.

Up until i blew the first primer i had exactly what you described, slight cratering and no flattening.

Its not the best thing to have happen, and i would never run a load that hot, but if it happens once it will not destroy the rifle.

 

[palmettoman]

Sounds like what I had going on with my 6.5 CM until I got the recoil spring changed out to the Tubbs spring for the AR10. It was kinda like Goldilocks. The first spring I had was too heavy, the second spring was too light allowing the BCG to start back a little too soon. FTE's galore and false pressure signs to boot (swipes and burrs). The Tubbs combined with a plain jane adjustable gas block solved it.

The other thing I had to fix was the primer I was using. The soft CCI 400's kept popping (not completely blown out of the case) and small pieces of primer would find their way into the BCG also causing problems. Switching to Fed GMM A/R primers solved that.

Now using the same loads, reliable feeding, no pressure problems.

Good luck.