Pressure Signs in a Bolt vs Semi

[Lucky Se7en]

I posted a thread a few weeks ago trying to see if anyone could help identify the culprit of a sticky bolt lift in one of my loads for my 308 bolt gun. It seems like the general perception was just that PPU brass was no good for multiple reloads. I plan on shooting an identical load out of some of my once fired FGMM brass to see if it cures my sticky bolt lift before I write the brass off, but it has me wondering about the other reloads I have in 308 PPU brass that I shoot in my SCAR. I have never really had any pressure signs with the brass other than a sticky bolt lift, the primers and the brass both indicate that it is a very mild load. I am having a hard time telling myself that the load is no good for my AI bolt gun, but perfectly fine for my SCAR. Is there anything else you guys usually do to look for pressure signs in gas guns aside from examining the brass and primers?

 

[supercorndogs]

What load? What bullet? What velocity?

 

[Lucky Se7en]

168 grain A-Max about 0.030” from the lands with 41.4 grains of varget at 2500 fps and CCI #200 primers

 

[mi223]

How do they chamber? Any chance the shoulder is tight to begin with.

Sent from my SM-G930P using Tapatalk

 

[padom]

Sounds like a brass issue. Your scar probably has a more forgiving chamber which would explain why it runs fine in it.

what's your once fired brass in your bolt gun measure with a case headspace gauge??? How does that measurement compare to the brass your loading and get sticky bolt ? What's the length of this brass?? You trimming before loading?

 

[newguy2k3v2]

Did the rounds that gave you sticky bolt lift chamber easily?
My initial guess is you're not sizing them quite enough. The ai almost definitely has a tighter chamber than the scar.

 

[Lucky Se7en]

I'm not feeling anything unusual when I chamber them, I typically only neck size for the AI so at first I was wondering if that could be causing issues. I ended up FL resizing some of the brass and firing it in the AI and that didn't seem to help, might actually have made it worse. I recorded the headspace for my once fired brass in my AI to be 1.627" vs 1.300" in the SCAR. All my 308 brass is trimmed to 2.005" and I always trim right after resizing. Most of the longitudinal growth in my brass occurs during FL resizing, I'm not trimming much when I neck size. The brass that I fire in the SCAR is always FL sized with one of two dies, I have one die that will FL resize to fit in the LE Wilson headspace gauge (roughly 1.623" if I remember correctly) and another that will bump the shoulder back 0.002" below the AI headspace (1.625").

 

[Lucky Se7en]

Just shot the exact same load that was giving me a sticky bolt lift with federal brass and everything works fine with it, I can easily cycle the bolt while keeping an eye downrange. Looks like it's confirmed that it's the PPU brass that is giving me the problems. I'm still having trouble wrapping my head what exactly would make the chamber more forgiving on the SCAR.

 

[Sogan]

Thickness of brass can increase or decrease pressure when using the same amount of powder as well

 

[Lucky Se7en]

True, this is a load that started getting a heavy bolt lift abruptly that I couldn't cure by lessening the charge even to the minimum. It seems like the PPU brass is more effort than its worth for the bolt action but I have yet to see any pressure signs in the semi-auto.