A lot of "cheating" going on in Clint Eastwood movies!
Just from that relatively clear bottom picture above, that appears to be a cap and ball revolver, has no caps, and the hammer is down. Since it is single action, even pulling the trigger will not cause a hammer fall.
This is a fine example of how a real, safe, movie is made. The actor himself can determine that the gun is un fireable. Forget the nitpicking viewers such as my self who see the discrepancy. A good movie is important, but all the participants alive and well at the end is more important.