I used Fevereon prop's trigger/hammer design from a gun she built as the basis of my design for a moving trigger/hammer assembly. I built the barrel out of a top and bottom piece of wood, with the barrel heat sinks sandwiched in between. the heat sinks were made from various widths of styrene strips glued together. for some reason I cannot find any in progress pics of this step :(
I made the cylinder pretty easy, I found a pvc pipe that was already the right diameter. I found a nice selection of various diameter brass tubing at the hobby store and cut six pieces that fit nicely inside the pipe.
I filled it in with Apoxiesculpt and sanded it smooth. I have some brass pipe that fits perfectly inside the cylinder tubes to make some bullets with
Next up was the trigger guard, which I cut out of mdf with my tabletop scroll saw, sealed with shellac, and sanded smooth. Sealing the mdf with shellac keeps it from tearing up while sanding, and makes a nice smooth, non-porous surface for painting and molding I have seen where some prop builders paint on a coat of super glue for the same purpose
So, here are a few more pics of the whole gun,