There is such a thing as a brush gun. It is a short, light weight, quick handling little rifle that is easy to carry around and quick to get a shot off with.
Now, there is no such thing as a brush bullet. If a bullet hits brush of any kind it will be deflected.
Some great brush guns are the Marlin rifles (I have the 444 marlin) and Ruger compact M77's (I like the laminate compact).