I think you might be better off making some practice guns first. No offence, but there are a lot of flaws that you just won't be able to improve. I'd advise you to find some other guns, and make models of them, sharpen your skills, get a solid technique going - and then do your game models.
To sharpen your skills, I suggest looking at some FPSC gun models, figure out how they're put together. It's not a good idea to break a gun into basic shapes, break it into it's components instead. It's ideal to get blueprints for the guns that include an exploded view - or at least blueprints that make the detail not shown on side views more obvious. Be very strict with yourself, if part of your gun isn't working out, delete, and do it again - it's better to maintain a high quality than to try and enforce quality at the end.
Keep practicing, tackle each gun as if you were defusing a bomb, and you won't believe how much better your guns will turn out.
Health, Ammo, and bacon and eggs!