While there are quite a few varieties of 45 ammo on the market, the 45GAP round will not work in the Judge revolver. Along with the markings on the gun, the manual will tell you the rounds needed. The common round used for the Judge is the 45LC also known as the Colt 45.
Here is a quick rundown of the common 45 ammunition rounds.
45ACP -- Used in semi auto pistols including the popular 1911 and other modern pistols from Glock, Sig, Springfield etc.
45GAP -- Used in semi auto pistols made by Glock. This is a shorter round designed to fit a few models designed by Glock. May not be interchanged with the ACP nor ACP used in GAP.
45 Colt/ 45 Long Colt -- Used in revolvers or lever carbines. This round features a rim on the cartridge which is required for revolvers. This design will prevent the interchangeability of the ACP round.