This trick works very well against bots and players alike. For example, in the DM level "XJ5", there is the grated walkway where the rail driver is on the upper floor. Go down the other end (the one close to the hallway by the Envirosuit armor), and blow a hole in the floor near the grate large enough to get in and duck down inside. Be careful -- if you do it too close to the grated catwalk, then it will also break part of the bottleneck off and expose you from the outer wall, being that it was blown out from the blast. From here, you can use any type of bullet-using weapon with ease. The rail driver is recommended, as it will allow you to duck down in the hole, giving you cover from most of the players/bots, but allowing you to fire at them through the floor/ceiling. This trick also works very well when you back yourself up against an indestructable wall, so you have a full peripheral view of 180 degrees all around, with no danger of being back attacked.
