I have sanding belts in rolls of 10, 15 and 20 ft, for a barrel that is is rusty I tare the rolls in three foot sections then tare it into to narrow strips and sand the barrel by making one loop around the barrel and polish, as the barrel cleans up, I repeat the process with a finer grit. For shallow pitted parts I use a file. Oil will aid in preventing rust, it will not heal the damage, To keep from filling the strips with dirt and degree a green Scotch brite pad can be used, then the barrel can be whipped clean then start with the strips, something like polishing a crank shaft, for polishing save the old worn strips.
F. Guffey