I've done the spiral ramrod with a flame. A plumbers small acetylene torch works. Set it on a solid work area and hold the ramrod in two hands, slowly turning it in the flame and progressively moving it at the same time. Don't try to turn it to charcoal, just singe it enough to color the wood. It can actually be sanded back off and redone, if you are unhappy with the result. I would try it on a cheap dowel first, anyway, just to get the technique down.
Then there is the method of cutting your own hickory switch the right size for you gun, and cutting a spiral of bark off of it, leaving the alternate spiral to act as the masking tape listed above. Once the switch has dried, you stain or burn the exposed part and then peel the rest of the bark off. I have not done this.