I think that's a great start myself.

You can also try mapping a texture from a real weapon onto your model- that's a technique used a lot in low poly modelling for games- this is a low poly rifle (requirement is under 350) I made for a game mod I'm fortunate enough to be helping out on (rifle in foreground, image being used as plane for modelling against in the background, texture is a 256x256 map made in PS). Using real weapon textures can help with getting a realistic look. Also if you try using a cylinder with a lower number of faces on the butt it can help with giving it a more rounded look. I tend to break the weapon down into parts and think what shapes would be the best start for each area before I start to model. I don't use the create poly tool as much for low poly work as you can end up with a bit of a square look.

Hope you don't mind me pasting a pic in your thread (bit over compressed and the parts are not merged together, but you get the general idea).