I made a dummy for M-1 carbine out of regular components, and put something or other in the primer, I think rubber. Well I was gonna sell a carbine I had not used for awhile at a show. The night before I was testing the function for any new issues. You know what. I went to the show and cleared the carbine at the entrance. Dink, dummy flies out, and it looks like real round. This did not impress the checker at all. But I proved it was a dummy and he let me in. Never tried that again. I put some red Azooms in a new sXs shotgun for dry firing and then stored it with those chambered. What could go wrong. I had cleaned and lubed and wiped down. Eventually I took the shotgun out and found the bright steel at the chamber mouths was turning. Like it was starting to rust. Maybe something in the metal or coating? Luckily was able to clean up the minor staining without any real rust or pitting. Now I leave nothing in it. I use the red plastic Italian dummy rounds alot. They work nice for awhile but either the spring loaded part breaks or the plastic separates from the brass base. I agree with drilling holes in DIY dummy cases for ident. That is how the old military dummies were made. As paint etc. will eventually rub off the bullet.