Yes, I tried that method, also. Not long ago I took a 22 rimfire on trade and later noticed I could hardly see through the barrel! I used to think a 22 rimfire would not lead, because of the lubricated bullets the loading companies used. In fact, in a lifetime of shooting, I never before saw a 22 barrel leaded up, and this one was extreme, plus.
I found the vinigar and peroxide formula. Being somewhat of a skeptic, I put some of the mixture in a small container, pried a 22 bullet from a cartridge and put it in the mixture. A few hours later the mixture was black and the bullet partly eaten. Next morning there was a black mixture and no 22 bullet.
Only thing was the instructions I got through Google, stated to only leave it in the barrel for a few minutes, it stated that some barrels could be damaged. Well, I had nothing to lose, the rifle was no good that way, so I plugged the breech end and poured the misture in the muzzle. Next morning about two thirds of the lead was gone. One more long session and what was left was easily taken out with a brush and Hoppes #9.
The barrel looks beautiful now.
Yup, works great. 50/50 mixture and be careful not to get any on the outside of the barrel, it will wipe the bluing off right now. I bought an old 30/30 , 1905 to be exact with a black bore for really cheap. I had to do the mixture all night before I got to where it was at least scrub able with a cleaning brush. Usually only 30 minutes is enough, if that, but this one was really bad. It took a lot of work but the barrel looks almost new when you look down it now and shoots great. Almost had to get out the mercury but I abstained.