I can only assume you have experience and know what you are doing, but even 30/30 pressures are twice (or more) times greater than this action was proofed to handle; so one must wonder if the metal around the firing pin holes and breech ball walls will be thick/strong enough to withstand the extra pounding without being deformed, cracking, or (heaven forbid) exploding. Given the relation of the eyes and brain to any major failure at the breech, I would certainly encourage you to thoroughly investigate the ability of the Smith achion to handle the strains of center-fire cartridges long-term. That said, this appears to be a very in-depth and advanced gun project, which I am sure you have already determined; so good luck if you go forward and please post pictures of the finished result when done. And by the way, the 30/30 properly loaded will do anything a 30/40 Krag will do; your only "advantage" will be the "glamour" of having an odd-ball caliber that will be tough to find ammo for if you ever get caught short while hunting in the boon-docks.