I was watching ol' Johnny Rowland on Gun and Gears TV the other night, and he made a point of demonstrating how you can shoot .45 ACP in a gun chambered for .460 Rowland - which is dimensionally close enough to .451 Detonics to be interchangeable, if chamber depths aren't too tight - because the extractor hook will hold the shorter ACP case securely enough for the firing pin to reliably reach the primer. I'd be more concerned about having to clean all the junk out of the chamber - also as with shooting .38 in a .357 - than I would with any safety issues. A .451 round won't chamber in an ACP, so you don't have to worry about that.