For BP, I only use them once and toss 'em. Leakage starts to show around the primer pocket and pinholes burn through just above the brass. When I started reloading, in about 1960, paper shells were all we had. Even with smokeless, we were lucky to get 3 reloads. The crimp would get so weak, the second shell would sometimes open up after the first shot and start dribbling shot out. This was true with a semi-auto and/or even with a twice-barrel gun. When AAs came out, we couldn't believe we could get 15-20 reloads out of them. Amazing!
