My M4A1 with a custom built semi-auto master-key shotgun. The SPAS-12 was too ugly, so I built my own magazine fed gun.
An M14 that probably weighs more than an M60.
I turned the P90 into a much coolor bullpup assault rifle.
The M24 sniper rifle is a formidable weapon, but at close range, this attachment can come in handy...