It is called Ed's Red. Find it on google if you like. CALLED "ER"
I mix 1/3rd each of Mercon Dexron Trans fluid, K1 kerosene and mineral spirits (paint thinner).
For lead build up clean as normal with brush and ER and then run a sloppy wet patch of ER in bore and place muzzle down on paper towel propped against loading bench or whatever.
The run a tight patch down bore after about 30 minutes soaking and you will see slivers of lead come out. ER will penetrate under the lead and release it.
I leave bores coated with ER. I had one rifle I left 14 months with wet bore and bore scoped it. It was still quite wet with ER.
I get a 2 gallon Blitz can at Wally World and mix 2 quarts of the above so wind up with 1.5 gallons of it. Cost will be maybe 15.00 with can, and other stuff required.
I have it in lab wash bottles and industrial spray bottles (from Home Depot). I use it for many applications including killing fire ants. Just kick the mound, get them all agitated and lightly spray those you see running around. Come back an hour later and kick mound and none will come out. Mound is dead. good on wasps, locks too. won't gum up.
Try it, don't think you will go back to anything else.
Hummer