[Unclenick]

Without inspecting the brass, it is hard to say what the issue is? If you have the rough chamber Harry suggested, you will probably see shiny spots on the case where it was dragged out against them. Often these show up as bright rings around the brass because the roughness is circular gouges created by improperly lubricated reamers being run in too quickly and without adequate chip wash-out. If you have high pressure, the fired cases will be difficult to put back into the chamber after firing but before resizing. The dry fire suggestion is good in case the problem is in the bolt as described earlier. Look for a crease at the case mouth in case the chamber neck is short. If your dad was working on it and it is a replacement barrel, he could have got a short chambered barrel that has never been finish reamed and therefore has no throat. That would make for some high pressure, though I should think you feel it when you inserted cartridges. In addition to having been made all around the world, these guns have been gunsmithed all around the world, often by amateurs looking for an inexpensive surplus gun to learn on. Having a qualified gunsmith inspect it might not be a bad plan?