If the owner's manual indicates that you should not use any cleaners with ammonia I guess I would have to question the manufacturer as to why. What the hell did they make the barrel out of - plastic? Traditional barrel steel is either carbon or stainless. I have never hurt any of my match grades rifle barrels using Sweets. Over they years I have found that if a barrel is heavily copper fouled only ammonia based solution will take the copper out. Be advised, however, that strong solvents like Sweets can only be left in the barrel for a short period of time (follow the directions) or it can actually etch the bore. I definately would not use a stainless brush especially in a carbon steel barrel. You are probably best to patch the barrel with the solvant and if scrubing is necessary use a nylon brush. The solvant will eat a bronze brush. Good luck.