Crash Maniac
which would explode the potato after the first shot...
fail.
That's why you change off the potato after each shot.
Ever seen
Shooter? The main character snipers a bunch of guys from a boat with a .22 bolt-action rifle, using potatoes as silencers.
The potato's not the only improved silencer you can use; anything that'll trap the gas without blowing the barrel works. One guy in
The Good, The Bad and The Ugly used a pillow as one, and Jack Bauer used a rag wrapped around the gun in
24.
But yea, a potato on a machine gun would fail miserably.