Thread: believe it or not?

Originally Posted by gimp

From a .270 R700, factory Federal on the left, reasonable pressure handload with WLR primer on the right.

Yep, this is fairly common on R700 actions. It's not the size of the firing pin hole tho. The pressure is actually punching the firing pin tip backwards after ignition. Push pressure too far and the primer will 'blank' and rupture. (Nasty things follow....)
Cure for this is to fit stronger mainspring (some drawbacks with this option) or a reduced diameter firing pin tip size (I.e. Like what you will find on my Stiller custom actions ), or simply reduce loads a bit until primer stops pushing f.p. tip back.

This is one reason why guys start with a custom action like a stiller or Barnard for a new rifle build if they wanted to run slightly higher pressures with reduced risk of blowing primers. ( note I did not say NO risk.......).