Help with high pressure all metal cannon

[spudkpi]

It has been a while since I last posted on here and it feels great to be back. Anyways I need help concerning the new all metal cannon I want to build. I have a co2 setup with regulators and everything ready to go but what I am stuck on is how to make it semi auto. I cannot figure out how to design a blowback bolt or an autofed magazine. I would like to do some sort of a magazine with a spring or something like that. I plan on using mostly copper for the chamber and piston valve area. Also what is better to seal the copper: solder or epoxy? I really respect the opinion of my fellow peers here so any help would be greatly appreciated. Also any suggestions on easy homemade qev valves would be nice. Diagrams would help a lot because I am having a hard time putting this together in my head. Thanks.

[pizlo]

Solder>epoxy when done right.
Read up on all of JSR's projects as most of them involve the kind of bolt/valve you want.