The m16s are very bland and lack the pop-out they should have in a game like blockland. the 50 gray stock, body and magazine all kinda mesh together in a boring way. My suggestion would be to make the stock and magazine a lighter/darker shade of grey so it pops out as a 'different piece'
The rest of the guns are done well in terms of color scheme. The use of Browns and light and dark grey set the weapon anatomy apart from each other. The m16 lacks this flare of distinguishability. Also the bottom of the handle looks disgusting