SGW Gunsmith,
Try the modern chemistries. They are faster and more thorough than the ammonia in Sweets, which I used to use a lot on a grabby Garand barrel I had. But that was 30 years ago. Chemistry has evolved since then. I would never have believed the difference if I hadn't tried it myself and witnessed what it can do.
Part of the secret is the Bore Tech solvents are not used up by the reaction in the same way the ammonia and its oleates are. The strong part of the chemistry oxidizes the copper and then hands it off to a chelating molecule that binds to it so it can't redeposit in the bore, freeing the oxidizing compound to keep attacking the copper at full strength. It doesn't lose speed of attack or stop working until all the binding chemistry is packed full.
If you follow the link I put up in post #5, it takes you to a 2006 Precision Shooting article in which a fellow with a borescope set out to compare a large selection of bore cleaners, most likely including Sweet's, as it has been very popular in the past. But we'll never know, as, in the end, he found every cleaner he tried so inferior to Bore Tech Eliminator on copper that he decided it wasn't worth bothering to list them. It's pretty remarkable.
In the intervening years, Bore Tech has come up with more products, including a copper-specific and carbon-specific and moly-specific and rimfire-specific and shotgun-specific formulations. They've got a new gel that combines their chemistry with a soft abrasive to speed things up further, but I've not tried it, as just the liquids and patience seem to do the job quite well.
Also, if you have the time to kill, for all forms of carbon and moly, Gunzilla is hard to beat if you let it sit overnight. If you let it sit for weeks, it will remove all old carbon, even getting to the bottom of rust pits and clearing the rust out. Very good stuff, but slower and much less active on copper.