General Discussion

It's more than just scaling the bolt. Heavier bolt means heavier recoil springs. Heavier recoil springs means larger/stronger receiver. Magwell and magazines also have to change for each caliber. Magazine design is one of the most difficult parts of creating a self-loading firearm. It's easy to make one that functions; it's hard to make one that functions reliably (even when using an existing design as a reference). You can "cheat" and rely on commercial mags, but even then you'll usually have to tune the feed geometry since the behavior of a .45ACP cartridge is going to be radically different than something like a 5.7.

There is a 9mm version of the Decker 380 in development right now and despite the cartridge itself being nearly identical just 2mm longer, nearly everything except the fire control system has had to change to some degree.