I need some help with two things
 

First off how can you takeoff like the barrel of a challenger tank? Mine is 1/16 scale and has two BBs lodged near the start of the barrel in a position where I can’t poke them out and I haven’t been able to find a video showing how to remove the barrel of the tank, or the section of it. And for my second thing, my tank makes a terrible grinding sound whenever it goes off a wooden surface or any concrete or anything so dirt sand grass gravel. I haven’t been able to locate what is causing the grinding but I think it’s one of the back sides for wheels on the right hand side. If anyone has any ideas, please share thank you very much.

You have to take the top off the tank. Then take the turret off the top, then take the whole turret apart and remove the barrel.
about as far of a tear down as is possible. Sorry.
maybe take a long rod, hold the tank so it faces down and try ramming the bbs and see if the will fall out.
As for the noise, if you can’t find it keep driving. You will either find it or it will go away.