During the gun battles, none of the weapons recoil when they are fired. This clearly indicates that they are loaded with blanks.
This film takes place in the late 1860's, shortly after the end of the Civil War. Yet the U.S. Cavalry troopers and most of the armed civilians are carrying Colt Model 1873 Single Action Army revolvers. That firearm was not issued to the Cavalry until 1874, and it didn't became available to the civilian population until a year or two later.