[mrerick]

You may find that a replacement pin will break pretty quickly after you replace it.

I've had this happen in one of my Lugers. The problem is that there is excessive play along the length of the toggle train caused by wear. In the case of my Luger, the breech block pin area had excessive wear in the breech block and front toggle link holes. This slight looseness is enough to cause the pin to snap when the gun is fired. This may relate to headspace since the cartridge head ends up well off the breech face during firing. We're talking a few thousandths of an inch.

The solution is to use an oversize pin and to correctly resize the holes in the breech block and front toggle to fit the oversize pin. This eliminates the play between the breech block and forward toggle.

The breech block is hardened, so enlarging this hole is not trivial.