STOP. No, really- STOP
Do NOT try to shoot 22 rimfire in that. Unless I miss my guess, you have a rifle made to fire .22 CB caps. Usually 6mm, round lead ball, primer only, no powder.
Do a google search using terms FLOBERT and WARNANT. The breech was held on one side by one screw, swung over behind the cartridge. It is not strong enough to withstand the force of a standard 22, and it will auto disassemble, burying itself in your forehead.
I may be wrong, but every one I have seen with that distinctive shaped trigger guard was in that category.
If wrong, I apologize. If right, St. Pauli Girl (dark)