Commercially produced, so no slam bangs. 
Maybe a break action single shot like a Baikal, H&R or something similar? Perhaps a recoil operated semi-auto? By simple it should include everything, like the trigger group, and not just the action. What do you think? And would the most simple also be the most reliable?
Maybe a break action single shot like a Baikal, H&R or something similar? Perhaps a recoil operated semi-auto? By simple it should include everything, like the trigger group, and not just the action. What do you think? And would the most simple also be the most reliable?