RE: homemade blackpowder solvent?
There are lots of homemade cleaners. I wonder if you are thinking of MAP cleaner. MAP is a combination of Murphy's Oil Soap, Isopropyl Alcohol, and Hydrogen Peroxide. I usually mix it 20%, 40%, 40% in the same order. Others like to mix it 10%, 45%, 45% reducing the Murphy's oil soap. The thing with Hydrogen Peroxide cleaners are, they cause flash rust. After you clean the barrel with MAP be sure and get some dry patches down there and then oil that bore good.
If all you are wanting to clean is black powder fowling, why not just use Dishwater. Mix some dish soap in water, will clean out fowling just fine.
Another is a 50/50 mix of isopropyl alcohol and car windshield washer fluid.
Don't overlook simple household cleaners also. Simple Green and water makes an excellent cleaner. Also there is an orange cleaner you can mix with water and that too will clean fowling.
The problem comes when it is plastic, lead, and copper fowling you need to clean. Then you will need a brass bore brush and some good solvent like Butch's Bore Cleaner, Hoppies Black Powder Solvent, or Birchwood Casey Bore Cleaner.