The obvious possibility has not been mentioned. Head space for .45 ACP was created by filing the recoil shield. As long as the firing pin was not shortened it would drive .455 cartridges forward then set them off when their rims stopped against the rear face of the cylinder.

Even if used in the line of duty, owned by a LEO is not the same as having been purchased by their employer. Lots of cops own lots of guns over their lifetimes.