Note: An unpatched version of the game is required. Go to any mounted minigun on any level, then stay behind it and start to melee it. You can do this by yourself or get other people to do this. Every time your gun hits the minigun, its launching strength increases. Once you hit it enough, jump on top of it. One of two thing will happen: it will either make you bounce very high or launch you across the map to your death. Bouncing straight up on it allows you to get to unreachable places such as buildings, airplanes, barriers. etc.