Continuity goof with Rudy's handgun

I saw this film in the late 70's and enjoyed it, I still like it. But one thing that always bugged me was the way Rudy's handgun keeps changing from shot to shot during the final shootout in the hotel.

If you have never noticed then watch next time and you'll see that for most of the film he carries a Colt Python .357 Magnum with a 6" barrel. It's seen very prominently in several scenes. He still has it as the climactic confrontation starts.

However it suddenly changes for no apparent reason to a Colt Trooper .357 Magnum with a 6" barrel. He then uses both in alternating shots!

The Python looks very different to the Trooper as it has a ventilated top rib and a full length barrel underlug giving it a very front heavy look. The Trooper looks more conventional.

I know its a "picky" point and probably only something a gun "enthusiast" would pick up on, but I have always been curious as to why they did that?

Surely someone in the crew should have realised?