First off i love the term brush gun. What the hell is a brush gun. When you site in a brush gun do you do it with brush in front of your target? So you can take into account deflection and bullet fragmenting. All i have to say on the matter is that if you fatally hit a anamial with a bullet (or piece of a bullet) after the bullet hits brush it is just dumb luck. And just to add to the argument there have been more animals taken with a 30/30 in the state of maine then any other.
My Defintion of Brush Gun.....A gun that is used when hunting on the ground or sitting against a tree in a area where there is thick heavy cover where you don't watch the deer come in a parade around in front of you at 100 yds, for situations where you jump a deer and visibility is low and your shots on animal that you have spotted are quick and in close range. It has nothing to do with shooting through brush and over other obstacles its pertains to the area where you are hunting and what style of hunting you are doing. For example i hunt NH and most of the mountain is covered in very heavy laurel when following fresh tracks in the snow the odds are you are going to get a split second shot at short range on a deer and in that case you want a gun the will cycle quickly, pull easily and light enough to carry when your hiking through thick terrain.