That slow, low BC 30/30 will cut through brush. You see a Whitetail through a thicket and you don't have a clear shot, but you know about where those vitals are - the 30/30 gets it done.What makes it a brush gun? Shooting through brush hoping to hit something or easy to get around in brush?
I can't even type that with a straight face.
What makes the ubiquitous 30/30 an awesome "brush gun" (which it undoubtedly is) is the short barrel, ergonomic design and quick sight acquisition. It is far superior in thick woods because of handling advantages, not any ballistic related attribute.