Throughout the film, the gunshots make weak popping sounds that readily identify the cartridges as blanks. Actual guns of the period were mostly of .44 and .45 caliber, which were very loud when fired.
Spike gets the drop on Wyatt and points his pistols at him, pulls the trigger and discovers he s out of bullets. He throws down the pistols and jumps on Wyatt. During the fight scene you can clearly see the pistols still in the holsters. Later in the fight the pistols are gone.