Well I recently acquired a nice Spanish Mauser dated 1921 in 7x57 for a nice price. The bore was in less than stellar shape but I could see rifling (barely) with the naked eye. A lot of cleaning and scrubbing and I now have at least a little more rifling. There is still some sort of gunk coming out of it that I am not sure what it is but maybe a few rounds will help clear it up. Anyways I drove a lead slug from the muzzle and got .287 grooves then did the same with a different slug from the chamber and got .287. So not to bad. I tried to make a chamber cast twice with cerro safe and both times had to melt it back out as I couldn't get it to pound out. I know the bore is kind of rough but the chamber looked ok with my borecam. Is there another way to get a good chamber cast that will come out, do I need a chamber cast since I know the groove size? My intention is to shoot PPB in her so I'll need to find the bore diameter somehow. I did check headspace, with a go and no go gauge, and its good.