After being fired from a gun, bullets act differently than anything you would expect. They will act more like a football when hitting something than a baseball or pool ball. When a football hits the ground, it can go just about anywhere. But when a baseball hits, a fielder can play it off a bounce.
The pattern isn’t completely random. A bullet normally travels along a hard surface after hitting it. For example, let’s look at a street. If we shoot the street 10 yards in front of us, the bullet will bounce off the street and continue in about the same direction you fired it, but will travel 6-8 inches above the ground. It will also kick up a bunch of rocks or debris that will turn into projectiles. Why is that useful? The North Hollywood Bank Shootout in 1997 was ended this way. A SWAT officer laid under a car and shot the heavily armored bad guy in the legs, ending the half hour gun fight where over 3,000 rounds were fired.
The same thing happens when bullets are fired and hit a wall made out of a hard surface. This is why you shouldn’t crowd cover. Most of us use cover by standing on top of the wall and sometimes even use the wall for support when shooting. This is a major mistake and a good way to get shot or take shrapnel off of the wall. So when using cover, and you always should whenever possible, stand back from cover so that you don’t get fragments. The picture below shows how a little distance can be your friend.
Law enforcement will always tell you to back up so that someone around the corner or on the other side of cover can’t grab your gun without you seeing them. I don’t know if there has ever been a real case where that was a problem or just theory, but it sounds good.
I also stand back from cover because, in my experience, especially indoors, it makes it harder for you to be seen. One of the hardest things to learn in the military was to look past the room you are in into the next. Most people see the world this way, one room at a time. So if you are standing back from cover, you appear to be in another room and may not even been seen by the other guy. In the Marine Corps we called this the long angle.
The only downside there is from standing back is that you are further away from your target, but that’s also a plus. If the bad guy is further away from you, you are farther away from the bad guy. So it works both ways.
So when you practice, think about standing back from cover, and get with a friend and look at the long angles in your house.