I just finished watching the commentary version of Magnum Force, with commentary provided by John Milius, who wrote the script (and also wrote the script for the original Dirty Harry, I believe). If you get a chance to watch it, check it out. It's quite interesting. Milius is a gun person, and when he starts talking about the guns used and how they are used it's pretty good. He even mentions Jeff Cooper at one point.
For example, Dirty Harry's gun was supposed to be the 4-inch model, which is the model that Milius himself owned. But they couldn't find one like that to use in the movie, and the only one they could find was the 6-inch model. So Harry used the 6-incher.
He also points out that silencers don't work on revolvers, but that it's a common movie convention ("and they always just snap right onto the barrel--I don't know how they keep it from falling off"). There's lots more, so like I said, if you get a chance check it out.