[keystonearms]

Not that I might have the answer but I don't ID your meanings of '3 indents' & 'breech break'. Maybe I'm lacking something but I can't see 'indents' or 3 of anything.

In his next to last picture it shows the barrel face and there are 3 indentions there. Imagine a .22 Rimfire being dry fired and the firing pin left marks on the barrel.