All I know about Sweets and Barnes is they are strong, and I've always heard to stick with less than 30 min. of soaking, not overnight.
The major active ingredient is ammonia, which has been used to dissolve copper fouling for well over a century. Sweets and Barnes CR-10 have a lot of ammonia, mixed with water and some other stuff. If you actually read the directions, both advise not leaving a single application in the bore for more than around 15 minutes, otherwise it can etch the bore.
Some of the newer copper-cleaners include oil, which prevents this, and can be left in the bore indefinitely with no problem, though they quit "working" within a day or so. Some also don't use ammonia.
