Joerg Sprave, aka the crazy German slingshot guy, has left sling shots in the dust and concocted a Coke bottle gatling gun that no one should try at home.
Using old plastic pop bottles with pressure caps, a thin length of aluminum tubing and a half-inch valve, he pumps them to 120psi through the use of his bike pump then fits an arrow shaft (crossbow bolt?) over the tube.
And if one launcher is good, a six pack is better, amirite? Ho Ho Ho.
Of course, Joerg is in Deutschland and his new and increasingly long beard gives him mystical powers so avoid replicating his stuff at home under your own risk.