The great thing about third party compatible LEGO vendors is that you can buy different pieces and they all fit together with a bit of skill, and glue of course. Here we see a modified BrickArms M4 carbine, which out of interest is currently in use by US troops, and shorter and lighter than the M16A2 assault rifle.

This weapon has been modified with a pull out green magazine and cut out working iron sights from Tiny Tactical. The result looks really good and looks great with this custom minifigure.