Normally, the term " high brass" is applied to an ammuntion company' s maximum standard load. It has more powder and more shot than the inexpensive loads you are used to shooting (7/8oz vs 1oz) and produces higher velocity. The shot used is probably harder as well. All of these things combine to make the pattern tighter...forcing more shot down that slim little barrel, making that shot exit the barrel at a higher speed, and less pellet deformation because of the harder shot, which means they will fly straighter (and tighter). These same things may indeed make your shot string longer, as well, meaning that less shot may actually arrive at the target at a given moment than you would get with the lighter loads.

For most grouse hunting I' ve done, the lighter loads seem to work better. For chukar, huns and the occasional pheasant (longer shots at tougher birds), high brass loads get the job done with authority.

So-called " magnum" loads will magnify this effect even more. I have always thought that if a hunter needs a magnum load for a 20-bore, he should just go out and get himself a 12-bore and call it good.