Looks like most of the real gun type mods no longer work properly, as they complain about ammo type being null and such. Anyway this can be fixed?
Im having problems too. i noticed that idont think its possible with this system to change the caliber of a guns internal magazine (including just the barrels like how in a double barrel shotgun the barrels are the magazines). I was working on a shotgun break-action caliber adapter kit but i dont think its possible currently.