Rusty, what you have heard about air space in blackpowder firearms is true, because they have a tight fit between the patched ball or bullet, and the barrel. So if you have an air space, the projectile acts more like a bore obstruction, and can cause the barrel to explode. Like it was said before, with proper windage it's not a problem in a cannon or mortar, but I wouldn't want you to think you can get away with it in a rifle, shotgun, or pistol.