In Defensive Handgun II and one of their other more advanced pistol classes, the folks at Thunder Ranch had students shoot the guns of other students. In fact, we were to set up the gun with a malfunction, set it down, then the line moved down a few spaces and we were then ordered to retrieve the gun currently in front of us and shoot the target. We only had semi-autos, but we all got to shoot pretty much every type of gun there and one that was intentionally set up not to run properly. We did mags not fully inserted, bad rounds (dummy in chamber), stove pipes, double feeds, etc. It was the task of the shooter to make the gun run as quickly as possible.
Why? The folks at TR posed a good question. So you are in a gun fight. What makes you think you will be fighting with your own gun? They gave numerous reasons why you might not have your own gun at some point such as being in a secure area where you can't carry your own gun and you end up retrieving that of a downed shooter (cop or bad guy), gun breaks, out of ammo, gun taken from you, etc. During the course of action, then, you may be involved in a battlefield 'pickup' and hence be fighting with a gun that isn't yours. The gun you pick up may be discarded because of a problem that can be fixed, such as a malfunction. At the North Hollywood shootout, the first gunman to die had discarded his AK because it malfunctioned. He apparently did not know how to fix the problem and he discarded the gun. This was lucky for the LAPD as it was a simple stovepipe.
"If you look through your scope and see your shoe, aim higher."
-- said to me by my 11 year old daughter before going out for hogs 8/13/2011