please save as a jpg next time, paint will allow you to save as jpeg.
its a good start for a limbed based model, with new features coming in computer games in regards to physics and so forth will be great as your gun could literally break apart if it was hit by fire etc..
Currently in the game industry however things have been moved over to one limb making up the whole gun, this method is just as valid for speed issues etc..
The limbed method died off a little while ago but for certain aspects with new features it will make a comeback.