A speed modeling exercise that I undertook using a 2D reference image. You can see the original design, done by in Pimp My Gun here. Modeled in Blender 3D 2.66.0 in approximately 5 hours. Original design ęDan R. 2012, modeling by Douglas K. 2013.
When I made it, I was kinda thinking that the long piece you see on the "drum" in the centre of the weapon could function as a sliding safety, but I must say I didn't put too much thought into that either.