User blog comment:Cpl. Ross/If you could have any gun and any attachment at all, what would it be?/@comment-2047232-20100810212116

Some less stupid combos:

ACR with Care Package Marker Launcher (replaces Care Package Marker) and Extended Magazines. This combo would be useful when you want to get a Care Packake over a roof.

M16A4 with a Round Drum and Knife Launcher. Replaces the Throwing knife.

UMP45 with Ammo Magnet and Folding Stock. Grabs ammo when a weapon is in range, but you only get 25% of it back.