Joe Mantegna's changing gun

I just saw this for the first time in many years. I think it's a pretty good movie, but I was really distracted by Joe Mantegna's gun. The barrel length seems to change from shot to shot. And there's a cut in a scene in an alley where the gun changes from a revolver to an automatic! Since this was a major film with a property master, I assume it must be intentional. But why....?