Disassembly shows no sign of failure or wear. The pins are very tight, lockup appears very secure, and I have found nothing to indicate a failure of any type except for that little scar on my forehead. I have no problems with new cases, but once fired cases are a disaster. They all fail with few exceptions.

I was checking my notes when I was retrieving the load data, and in a 10-shot string of reloads, seven cases failed. Only one has ever caused a problem. None of the case head failures has caused gas to hit me in the face. Most of the case failures are not complete separations.

I "built" the rifle myself, and I did shorten (and re-taper) the barrel by one thread to eliminate any chance of excessive headspace (squared up the end of the barrel and finish reamed the chamber myself). When I finish reamed the chamber, I made one turn of the reamer at a time until the breach block would close on a GO. It has minimal headspace. When the block is in battery, it is actually in physical contact with the barrel face and the case head.

I know something occurred that was different from any other shot. A 1/4" long case head cannot pass between two surfaces less than 0.001" apart. But...for the case head to come out, the block had to be open, the hammer had to be retracted, and both went back into battery.

The only event I can conjure to create this sequence of events is that the hammer recoiled sufficiently to allow the block to move slightly to the rear and allow the case head to escape, but what force moved the block back into battery? THAT is the part that escapes me. The rifle has a thinned trigger spring (ala De Haas), and a primer could conceivably force the firing pin back hard enough to move the hammer, and subsequently the block. I just can't understand what force moved the block back into battery.

Jim