In a recent B-Rated Sci Fi film called Kill Command, the props department came up with this futuristic sniper rifle. It uses a backwards Magpul MOE rifle length handguard as a muzzle device. There is even a delta ring on the end of the handguard. It sticks out like a sore thumb.

You can see in the screen shot below, gasses vent out the accessory slots in the handguard.