The old method, shockingly, would involve plugging the chamber with a cork or rubber block of some sort and filling the bore from the muzzle with mercury. Leave it in overnight and it would amalgamate with all of the lead in the bore and clean it right out. This method actually is one of the best and easiest ways to clean the bore of deep and compressed lead. Of course, we don't use mercury for this purpose anymore because of it's toxicity but what a great solution to a leaded bore!

I have lots of mercury and, as a former chemist, have experimented and played with it carefully. Even taught my kids, safely, about the amazing properties of this metal. I have never used it in a bore, though. Too easy to lose some of it and contaminate something (like me.)

So, now we use bore brushes, chemicals and brass screens to pull through the bore to get the lead out. Or, as some do regularly, shoot a few full jacketed bullets through the bore to clean the lead out.

Kroil is nice and one solvent/lubricant I use at times. I love Sharp Shooter's Patch Out/ Wipe Out which can be combined with their Accelerator solution. Brownell's sells these. This will quickly pull out copper from a barrel as well as deep carbon and lead. Amazing to see the patches come out dark blue with copper when I use these products.

But, everyone has their fav. I use some Hoppes but there are better chemicals.