i think they look very good, however i will mention that guns don't normally slant down towards the exit shaft (not that ive seen) so they look a little odd. :) but theres nothing wrong with that. :)

Nicely done! I agree with chasersgaming.....the base shapes are a little off in places, well only the trigger handle and the front end look iffy to my eyes. The trigger handle may have lost shape when you upscaled the image. I would personally treat the front end as cylinder shape and build on top of that and alter it slightly if you want to create unique weapons. Just what I thought when I first looked at it :) Good job though!

The front end actually looks just about perfect to me- it does look a bit strange, yes, but it looks correct for an XM8- at least on the rifle and carbine variants. I'm a little less sure about the uneven spacing of the holes, and the shorter piece on the short carbine variant looks off to me. It might be better to make it more square, like a G36K handguard, even if it's not accurate.

I have mixed feelings about the radius at the front of the receiver; I hated it at first but it's growing on me. In the reference images I'm looking at the magwell is more squarish and rounded differently at the front. The butt also looks a bit flimsy, but looking at reference images it kind of looks flimsy on the real gun too.

If I wasn't looking closely and nitpicking, though, I'd think it was quite a nice piece of pixel art in whatever game I encountered it in.

Oh ye! I didn't realise its a real rifle XD...in that case you were pretty close to the mark. Its a really difficult weapon to draw and you did an excellent job. I took the XM8 challenge.....