I am a real beginner in this area, but at an IDPA course they taught me to stay back from the barricade and shoot from my normal stance, leaning out and keeping as much body behind the barricade as possible.
They told me that the reason to keep every thing, including my hands and my muzzle, back from the corner of the wall, is that: #1) bullets that hit the barracade (if someone is shooting back) can follow the wall right into your hands and gun, so you have a higher chance of being hit, which is exactly the opposite reason for using a barricade. #2) bullets that hit the edge of the barricade deflect off at an angle toward you. The closer you are to the barricade, the slighter the angle and the higher chance of you being hit.
So, if you want to be tactically correct, stand back from the edge of the barricade a bit, and lean out around it, exposing as little of yourself as possible, using NONE of the barriceade for support, just protection.
I do shoot amazingly well though from a rest against a verticle corner. So, if I needed to make a really precise shot and had time, I would use it. I was taught though to NEVER ever let any portion of your actual pistol touch anyhing but your hands. I am not sure I was taught this, but I will say that when I have put my gun itself against anything hard to shoot it, the effect is not good. I would be glad to hear discussion on this, because maybe I was taught wrong. I was taught: From your normal grip, put the back of either hand against the barricade as a rest. Works for me.
Another method is to use your support hand and put it up on the barricade as a rest, palm against the barricade. Like a Policeman signaling a car to "stop" you have your arm out, palm out forward, and your fingers all straight up and your thumb out to the side. The palm and fingers go against the wall and your thumb sticks out at a 90 degree angle. This is your support a you lean forward against the corner of the wall. Put the muzzle of your pistol in the crook of your thumb and use that as your support. This is slow but is very acurate for precise shots (for me anyway).
It is good to point out things that seem obvious, like "never block the ejection port". Sometimes until you try it, the obvious things aren't so obvious.
When I started shooting an IDPA course, there was a barricade and three pepper poppers. When the timer went, I popped out around the left-side barricade and started engaging the three targets from left to right. OOPS. Very tactically incorrect. The barricade was on my left, and as I came out around it I was supposed to engage the targets from right to left, as they appeared as I sliced the pie. I am glad for things like the IDPA, because you really need to try this stuff out against some pressure (the time clock) before you think you know how to shoot tactically. It is easy to make a really stupid mistake.
[This message has been edited by Red Bull (edited December 07, 1999).]