It looks nice, but-
--Trigger is misaligned.
--if you're modeling this with some real-life detail or reference, there's no break on the gun so it can reload
--Too many polygons are used to round it out, which isn't all that good of an idea
I feel like you're trying to be detailed, but you're almost too detailed on here.
I made another model similar to yours that shows some difference so you can see what i'm talking about.
Also, I'd look at pictures of guns regularly, not just from the side either. It's good every now and then to see what an AK looks like if it were shown from an angle.
Another thing, don't just extrude and whatnot, try using the merge tool to merge vertices on certain points.
That's how I got the buttstock to work, it was seperate from the model, then I just started merging vertices together.