$65 M16A4 Low-poly 3D model by Raider3DWeapons. Available on CGTrader with 41000 polys and 35000 vertices. Check it out on CGHub.
PNG (PNG, filesize: 764 MB), BLEND (Blender, filesize: 8.25 MB), FBX (Autodesk FBX, filesize: 2.6 MB), MAX (Autodesk 3ds Max, filesize: 8.72 MB)