Watched an episode of a Canadian cop shop show while snowed in - Cold Squad, I believe. Anyway an old murder was from a ".38" wound, a .357 had been recovered recently, and the forensics person was explaining to the cop that it could be the same firearm, since ".38's and .357's have the same barrel size" !
See, who says TV isn't educational !?
My wife tapes her soaps during the week and watches on the weekend - so yeah, I sit through some of 'em with her - the gun in the hand of the "bad guy" changed from a blued pistol to a nickel/stainless revolver in sequential scenes on one of 'em ! Whatever the prop guy picks up first, I guess.