In the photo you can see where the ejection rod should go. In most films there are several similar guns on site in case of a breakage. Maybe the guns weren't completely identical.
"It ain't dying I'm talking about, it's LIVING!"
Captain Augustus McCrae

I finally got a good look at Gates' six-shooter. A little over 14 minutes into the movie, as Gates is closing in on the runners, there is a close up. There is no ejector rod. Either it's been removed, or the cylinder swings out to eject empties and reload. I still haven't identified the model.
http://i2.photobucket.com/albums/y35/efs2/GatesHandgun-1.jpg
Somedays it's just not worth chewing through the restraints.

Ah. I see. I'll try to look a little closer next time. Thanks.
Also, FYI, "Peacemaker" is just another name for the Single Action Army model.
Werewolves Ate My Platoon!

In one close-up you can see the ejector rod- a nickle-plated 5 1/2" barreled Single action Colt is what it is.
"It ain't dying I'm talking about, it's living!!!"
Augustus McCrae