Yes, you can soak your Glock barrels in M-Pro 7 gun cleaner. I do this regularly. After I shoot my Glocks, I remove the barrels and drop them in a Tupperware container filled with M-Pro 7 gun cleaner. I let them soak for about 10 minutes and then run a few clean patches through the bore, then lubricate. Done.
Yes, you can soak any gun parts in M-Pro 7 gun cleaner for as long as you want BUT 10 minutes is usually all it takes. A 10 minute soak resulted in 100% removal of carbon and powder fouling in my gun cleaner tests.
Yes, M-Pro 7 gun cleaner will clean any firearm that uses black powder.
The best way to clean a black powder gun is to first remove any unburnt powder by dry brushing the bore. Then spray a liberal amount of M-Pro 7 gun cleaner down the bore and let it soak for 10 minutes. Now you can run some clean patches down the bore. Done. You won’t need to use a bore brush.