Hi there, you have a nice starting on those weapons but they don't look as good as they could look.
First of all, if you want to keep a bit of realism you should really look on the details of the weapons, for example the Ak mag (which is never straight.
In therms of proportions they look a bit odd, the M16 has a too small body in comparison to the stock, front guard and carry handle, try to keep an eye on that, and the same happens with the M249, but in this case the stock.

If you want me to give you some more advices just pm me, I'll give you more information. I've been drawing weapons from this size for some years and I could help you out.

The robot looks really cute and nice but could use some work, I can barely differenciate it's upper body parts.