H2Andy, it appears that H&K have a model they designate the USP. It comes in several calibers. I didn't know that, since I pay little attention to modern handguns.
Still, it's a bit confusing to say ".45 USP", since there is no such caliber. I suppose it should be called an H&K USP model chambered in.45 ACP. There are several .45 caliber cartridges besides the ACP. The Long Colt, the .455 series, etc. The letters or numbers that immediately follow the caliber, or diameter of the projectile, usually identify the kind of round, not the kind of weapon firing it. 9x19, 9mm parabellum, 9mm Kurtz; 9mm Long, 9X57; 7.65, 7.7, .30-06, .30 Carbine; etc, etc. The few times a cartridge is identified by the weapon which uses it is an informality, and generlly limited to cartridges fired only by that one weapon. There is a clear protocol: manufacturer, model, caliber. You don't mix them up if you are trying to be understood.
45USP must be an analysis of malt liquor.