Yeah, I agree with Travis.
That's not a good way to make guns, sorry, and don't take this the wrong way because it's coming from the mouth of someone who went through the same cycle. I'm gonna drop in some pointers and I hope they help you or anyone in the same boat.
Failure to prepare is preparing to fail. You haven't designed that gun, it looks like you've made it up as you go along. You can of course build the gun however you see fit - but working blind is not a good practice. Take time to sketch out your gun, first from an engineering standpoint, then from an aesthetics standpoint, and then from a practicality standpoint. Sounds like a lot of faffing about but really it isn't. Draw a little sketch of your rifle mechanics. Where does the bullet get fired?, how would the magazine load a bullet?, what parts would move when firing a bullet?... making a mechanically viable weapon model takes time, practice, but it's a different sport to what your doing. The last weapon I did was a 1911 - and it took about 2 weeks, me with a real size airsoft 1911 and a set of digital calipers (micrometer). I went through the whole mechanics, slide, bullet handling, everything to make that gun on the screen behave as much like it's real life version as I possibly could. The more time you spend on mechanics, the more rewarding it is at the end of the day, when you have this things that behaves like a real gun. FPS fans love their guns, and they love them to act like real guns. If your going to the trouble of making a weapon, then it might as well be a proper model. You'll notice polygon counts creep up when you have to add moving parts, internals etc - but it's all worth it. When I see my 1911 slide pull back and engage the trigger, I can see the next bullet to be fired, I can see the last shell discarded... without that attention to detail, my 1911 might as well be made from wood. Even though it's easier to replicate a real gun, you still have to keep it all in mind when making your own weapon designs. The weapons in Halom or Unreal for example are very tactile, believable, visceral - just what you want for your own designs.
I suggest watching a lot of FPS Russia, and those gun shows 'American Guns', and 'Sons of Guns' - you'll see the mechanics behind a modern weapon clearly, I'm sure that would help a lot.
So... first thing - how does your gun work, sketch out the internal mechanics of your gun - even if your not gonna model it. What you should end up with is an idea of how it all works, how the magazine works and where it should be, how bullets are treated, ejected etc, and the start of the basic shape of your gun.
Once you have that, then put the aesthetic skin over it, using existing guns as inspiration. For example, cooling chambers for barrels, modern stocks, rails for scopes etc etc. That's what the pro's do. Consider the gun you've got there - it's pretty wide down the whole body, and that's a mystery - there's no reason why a gun would need to be that wide all the way down. I mean, maybe there's very little mechanics after the clip - so it should then go into the barrel, with a heat shield or something instead of the longer body - like a carbine perhaps. Also consider how a real soldier would maintain the gun - clean it, unjam it etc etc - often that can be achieved by concentrating on components that fit together, rather than a whole gun. A scope for example - typically every modern gun will have changable scopes, it's usually best to just go with that - make your scope seperately, and attach it as if you were putting it on a real gun.
Lastly, once you have some sketches, maybe even a basic framework for your gun modelled - you should continually keep the guns usage in mind. If your adding a cool detail - make sure the player gets to see it - add things mostly on the left hand side of your gun - don't skimp on scopes and triggers - consider what parts of the gun the player would actually see, and spend your polygons there.
Anyway, I hope you get what I'm saying and keep at it - remember that function is more important than appearance when it comes to guns - an ugly but realistic gun is better than a gorgeous gun that doesn't make mechanical sense... Remember Half-Life, the MP5 in that had a little keyring thing that bounced up and down. Probably only 60 polygons, yet I remember that for years and years, 60 polygons in the right place can make a world of difference.
Keep at it, I'm sure your models will get better and better really quickly - practice, and above all; never model blind, always work from sketches - the instant you do that you'll notice a huge improvement in your design. It gets to be really good fun, making models like that - there's a real sense of achievement in making a believable model, probably a bit like being a gunsmith for real.
I got a fever, and the only prescription, is more memes.