Many players have asked me how I do some of the things I do with the gauss gun, so made this tutorial to try to teach them as best as I can. First off, you should be aware of the bugs with the gauss gun in Half-Life: Source. You can find that information here: http://developer.valvesoftware.com/wiki/Half-LifeDeathmatch:Source_Bugs. Incase you don't understand what a displacement surface is, here is some information on those as well: http://developer.valvesoftware.com/wiki/Displacement.
Anyways, my gauss technique. First off, avoid the primary fire, it is weak and depletes your ammo supply very quickly. You rarely see me use it, as charges do much more damage for the amount of ammo used. The first thing you should know (you will certainly know this if you have played single player Half-Life or original HLDM) is that charge shots from the gauss fire through thin walls. The shots are actualy spread when they are fired through a wall, making it easier to hit your target. Therefore, it is good to wait for your target to get behind a wall, then fire. You can also use this if someone is on your tail. When you go around a corner, fire through the corner and the shot may hit them. Also, you can use this to hit someone that is on the edge of a platform. A great example of this is on dms_spookface1. Along the outer paths where people like to snipe from is an easy place to hit people with the gauss. I usualy wait for someone to get behind one of the thin walls then fire, but also shooting the thin ground on which they are running will damage if not kill them. One last thing you can do with this trick is if someone is standing on the edge of a platform, fire at the platform right below the edge so it goes through the edge and hits them (see Screenshot A). Last, but not least, remember, the floors of raised ground are walls as well and can be fired through if thin enough (see Screenshot B).
Now the thing that tends to get me accused of hacking from those that don't know it. Displacement surfaces "explode" charge shots. This explosion has quite a range. Therefore, if you fire at a displacemnt surface and someone is on it and near the shot, they will be damaged if not killed. This is how I make most of my kills in dmsbuddaarena/dmsbudda2arena, as all of that grey stone is displacement surface (see Screenshot C). I wait for someone to get on or near it, and then I fire. This also works when someone goes on a bounce pad because the entire ceiling is a displacement surface, so I wait for someone to be near the top of their jump and fire at the ceiling near them when they are at the top. If it does not kill them and they fall near a wall which is a displacement surface, fire at the wall while they are on their way down. Also, the entire ground underwater is a displacement as well. You learn displacement surfaces as you mess around with the gauss on a map, then you memorize them.
Third trick, and one I am surprised more people don't know/use: gauss jumping. There is a reason the gauss kicks like it does in multiplayer Half-Life, and that reason is to let you jump. It works kind of like a jet back, you charge up, fire, and you get shot in the opposite direction in which you fired (see Screenshot D). There are two things you can control with this: one is the power of the jump (how high you charge the gun), and two is the direction (what direction you aim the gun). You learn to control these two things with practice. This is a great way to make a getaway or to quickly jump out of water (unless the ground below the water is a displacement surface). You can also use this to stop falling damage. If you have a relatively high charge and u fire it down when your about to hit the ground after a big fall, it can slow you down enough to stop taking damage (as long as the ground isn't a displacement surface, in which case you'll stop the falling damage, but take in plenty from the displacement shot).
General gauss technique:
Avoid attempting to hit your target directly, anticipate your enemy and wait for a good shot such as through a wall or on a displacement surface. Basicly, wait for a good shot or you will waste ammo (which depletes rather quickly).
Memorize your maps. Memorize reflective surfaces. Reflections are your worst enemy. Unlike firing on a displacement which will weaken the shot a bit, firing on a reflective surface will just send the beam back at you at full force, which will do a lot of damage if not cause a suicide. Also, memorize displacement surfaces, as these are greatly to your advantage.
Don't be afraid to hurt yourself. If you are on the ground and you see people fighting on a displacement surface, join them and fire straight down (if you have enough health of course). You can kill several people at a time like this. Just make sure if you do this, you aim in such a way that you will gauss jump to a good location as you will be low on health from damaging yourself.
Try to get high in the air if you are fighting near ground that is a displacement surface, this way you won't get hit by your own shot. Gauss jump to stay long in the air if necessary (as long as your not too close to the displacement surface).
Gauss jump to take shortcuts when after a target or making a getaway.
These are the two most important things when using the gauss: 1. Anticipate your enemy, then you can wait for a good shot and not waste ammo. 2. Knowing your map so you don't accidently kill yourself.
If I think of any other parts to my technique I forgot to mention I will certainly post them. Enjoy!