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Pressure issues please help

Grizzgup

Private
Minuteman
Mar 2, 2025
3
1
PA
Hello,

I have a BCM AR with a Rainier 18” barrel. I was loading 24.0g of N540 with 75g Hornady BTHP at 1.847 CBTOG with CCI primers, and it was great. Due to some unrelated light primer strike issues I switched out the bolt and BCG, and all of a sudden I’m getting signs of over pressure on the primers. Can switching the BCG cause that? It’s also getting warmer in PA, but I think N540 is supposed to pretty temp stable. Any thoughts would be appreciated! Thanks.
 

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Hello,

I have a BCM AR with a Rainier 18” barrel. I was loading 24.0g of N540 with 75g Hornady BTHP at 1.847 CBTOG with CCI primers, and it was great. Due to some unrelated light primer strike issues I switched out the bolt and BCG, and all of a sudden I’m getting signs of over pressure on the primers. Can switching the BCG cause that? It’s also getting warmer in PA, but I think N540 is supposed to pretty temp stable. Any thoughts would be appreciated! Thanks.

That looks like an oversized firing pin hole

Light primer strike issues shouldn't be caused by the bolt, were the cases sticking or not going into battery?

I don't know what 1.847 amounts to but the 75gr bthp hornady shoots great at 2.25" which is about where the cannelure usually lines up

You did check headspace...right?
 
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