I make my barrel applicators out of flannel sheet material. I tear off a strip of sheet about two inches wide and cut it about 20" long. I make a roll out of the strip so that it ends up being about 1/2" in diameter and two inches in length. Having polished and degreased the barrel with Comet household cleaner and a piece of ScotchBrite, I suspend the barrel on its pegs on two wooden V blocks, and I never touch the barrel with fingers again til it is browned.
I pour a shot glass full of browning solution, dip the end of the roll into the liquid, squeeze out any that will flow, and apply the roll to the barrel flat, moving evenly in one smooth slow stroke, end to end. Never go back to get places you think you have missed, especially with LMF Browning Reagent...you'll catch those spots on subsequent applications. For sight slots, I use a Q tip. For lock plates, butt plates, trigger plates and the like, I use two cotton balls (purchased at local drug store)
again, dipping and squeezing out excess fluid.
I have several methods of carding, ie: 0000 steel wool, Brownell's soft wire wheel on slow speed, often just a roll of canvas, using the end of the roll to scrub away loose rust.