I just fired my Collath and learned that C4 of the C4=8M (seen in pic above) means Collath #4 round. The gun fits me like a glove and performed flawlessly,,,,I LOVE IT. I should have guessed that it was in the Collath #4 but the 16 ga gamebore vintager round performed perfectly. As you can see the shell in the top pic, it was fire formed to the conical shape of a collath round. It was not mangled or split in any way.

I am now concerned that the 8M may be a Collath round. I will this weekend cerrosafe it to check..I hope it's 8x57JR.

Would anyone suggest shooting a regular 16 2.5" vintagers in this gun is dangerous or furthermore once fireformed should not be reloaded?

Thanks for your thoughts here.