Is there any calibre that is a real "brush buster"? I don't think the calibre is as important as the style of firearm. The lever action is as good as it gets for thick, tight areas. I find myself using a 3" 12 ga. slug in a 22" rifled barrel Rem. 870. I like this setup because it anchors a deer up close and you don't have to guess where it went.
I agree that type of action is better than style of bullet for busting brush. My son and I use a 30-30 Marlin 336C and 30-06 autoloader for heavy dense cover. Bolt action comes into play for more open territory.
As I sit and glass, which is common for hunters out west, I have sort of quickly discovered something I never learned when I was younger.
In my youth I had enthusiasm and spirit. In my middle to advancing years I have creaky knees, arthritis, and I tire more easily than I used to. Where I used to sit on the cold hard ground I now look for that soft spot to sooth my tired muscles. That leads me to my tip.
Carry your soft spot with you!
In my pack I carry an air filled, ultralight, camping pad....