I would not be afraid of the acetone/ATF mix. Have used it many times. Kano Kroil is THE best as far as commercially available products. Acetone/ATF works even better.
I had a guy bring me an old side-locker (Hawken) rifle he got and it had been in a barn (here in Michigan) he said at least 10 years. No case, leaned against a wall. Wanted me to see if I could save it. I soon realized it was still loaded. I tried several things to no avail and had to let it soak with acetone/ATF for a couple weeks to finally get the patch/ball and powder out. I finally got everything out and unbelievably after all that, the barrel was not all that bad. No pitting of any real significance. No need to go into detail here about what I did to get it nicely cleaned up but "the labor of love, working the barrel and time" was a big factor. Some things just can't be rushed. I managed to save the gun. He was thrilled. I loaded/shot it several times before getting it back to him and it had no issues.
Acetone is not "scary". It is simply a solvent. I use it to clean up dried contact cement doing laminate work. It's the main ingredient in nail polish remover and your wife/gal probably has a bottle around the house somewhere. Comes in plastic and metal containers. It is stinky and flammable.
Don't get any of it in a cut on your hands or you'll dance around like when Grandma used to put Merthiolate on your cuts when you were a kid.