Type 38

[Patrick Chadwick]

don't know about the ruptured primer, the firing pin protrusion dosen't look excessive,

The protrusion is probably not excessive. Firing pins tend to wear and become shorter, not longer. This effect (which I believe was once upon a time described in detail by jmoore) is caused by the case being undersized for the chamber. When the rifle is fired, the case is rammed forwards at the same time as the primer is ignited. The fully forwards case now expands to grip the case wall as the charge burns and the gases expand. The pressure forces the primer back out of the pocket. When the bullet has left the case, the pressure eases off just a tad, so the case loses its grip on the chamber wall and is forced back, thereby spiking the primer on the firing pin, which remains quasi-static because of its mass inertia. The primer often looks as if it had been subjected to excessive pressure, but that is not the explanation in this scenario.

The answer is to first load the cases with a fire-forming charge, and/or use the O-ring trick (jmoore pat. pending, I think!) to keep the base back against the bolt face. Once the case has been stretched, then only use neck sizing from then on. And don't bother going to a gunsmith and asking him to check it with CIP/SAAMI gauges. ACWOTAM as far as I am concerned. So many Ariskas show this bulged case effect that I really doubt whether those chambers were cut to anything like the modern specifications. As a shooter of ancient BPCRs you learn to take this sort of thing in your stride, and treat each antique as if it had its own unique chambering!


Patrick