The books says that's a rolling block action. If so, it should look similar to this.
Kinda looks like it has two hammers. The one in the back is the actual hammer. The front one is what holds the action closed. You cock the hammer, and then pull the front lever back. The breech-block rolls backward, exposing the chamber. The thumb-piece on this gun has been broken off, and a new piece is in the process of being welded on. That's why this one looks so strange.
Meddle not in the affairs of dragons, for thou art crunchy, and taste good with catsup - George of Lod, Year of Our Lord 297
I always take precautions.
Beware the Evil Bullet Fairies.