looking good. I would build the full hammer ( and the indent area it sits in), then animate the entire thing as one mesh. I'm thinking around 5 ish animation scenes

1. prime hammer ( rotates the cylinder, hammer moves back, trigger extends forward )
2. fire ( squeze trigger, hammer falls, (recoil/kick? or save this part for the arm animation?)
3. open cylinder ( dump spent cartidges)
4. load new cartridges ( close cylinder )
5. spin cylinder ( use occasionaly for a little bit of flare/fun)

model does need its rear sight, looks a little off without it.

but its a nice example of how your skills have improved so much since your tommy gun model