[Unclenick]

It's an abrasive impregnated cloth. 400 grit aluminum oxide abrasive applied to the cloth with a petroleum carrier like diesel fuel, IIRC. I read the patent once when Father Frog was looking to find a way for people to make it for themselves.

If you have a shiny bore after shooting a jacketed bullet through it, try my experiment making one pass with a clean bronze bore brush and see the shine gets dull. If so, you have nicely ironed-in lead. I used to shoot jacketed bullets post-lead until I discovered this test. It turned out the jacketed bullet was doing more to create the illusion the lead was gone than actually removing it. Obviously, over time, some portion will start being smoothed all the way out at the end of the barrel. You may reach equilibrium with your lead level that way and many guns will tolerate the bit of extra pressure just fine, same as they will tolerate a certain amount of grease in a bore.

I doubt that this practice is often a genuine hazard. That potential would mainly be there shooting into a very heavy lead accumulation. But as I said before, just use the No-Lead product and there really won't be any lead left. And the effort involved in patching it in and waiting an hour is pretty minimal as compared to the elbow grease involved in mechanical removal.