Why use the slow and heavy 45 ACP as a rifle round? The round is designed with fast powder to work well in a 3-4 inch barrel. Shooting it from a rifle barrel doesn't do anything useful. It flies slow, so it is hard to use at intermediate ranges (bullet drop at 100 or 200 yards must be difficult).
The 9mm as a rifle round sort of makes sense; it is supersonic, and there are special loadings (like the Swedish SMG rounds) that are designed for longer machine gun barrels, yet can be fired from handguns. The 5.7x28 is explicitly designed to do reasonably well in both handgun-length and carbine length barrels. But the 45 ACP just makes no sense, other than as a plinker. And for that, 9mm or 22 is just a better idea.
