HiBC,
Usually the ammonia issue comes down to concentration. It's actually a gas that won't harm metals, but we dissolve it in water to from ammonium hydroxide (aqueous ammonia) whose highly basic OH- ion can attack metal. You hear various estimates of what a safe concentration for barrel steel is, but there seems to be general agreement that over 10% ammonia dissolved in water is bad. Less so for stainless than for chrome-moly. Some say 5% or less is totally safe. I talked to one chemist at an ammonia manufacturing operation years ago who said they would actually add several drops of ammonia to water stored in steel drums because it inhibited rust. So a little bit can be a good thing.
Note that you don't want to confuse aqueous ammonia with ammonium oleate. The latter is a compound in Shooter's Choice and in blue Flitz and other products that dissolve copper more slowly than aqueous ammonia does. In general, the oleate will patch out green, while aqueous ammonia patches out blue.
I thought I saw some signs of bore etching from long exposure to Sweet's 7.62 years ago. It has some concentration of aqueous ammonia plus water miscible oils and possible other powder fouling solvents to prevent corrosion. But it may have been little more than just exposing an already rough bore. On the other hand, long exposure to Butch's Bore Shine caused me to see no problem. I could plug bores and let them soak in it overnight with no issues. From the smell, I would guess Sweet's has more ammonia, but I don't know for sure or, if so, how much more? I spoke with the inventor of Butch's on the phone when it was new. He said he'd submerged a piece of steel in the stuff for six months and microscopic examination showed no etching. So that product clearly doesn't do damage even in a plugged bore.
There is no question that non-stainless gun barrels treated with aqueous ammonia alone can rust because, as your grandma knew, aqueous ammonia is a fabulous degreaser and will even strip floor wax. It will remove any petroleum-based protection from airborne humidity the steel might have had in it. That's why Sweet's and Butches Bore Shine and other aqueous ammonia containing bore cleaners have water miscible oils in them. They leave the bore protected after the ammonia gas evaporates.
Some people like sudsy ammonia because the soap in it offers some bore protection. If I were charged with creating an ammonia-based bore cleaner today, though, I would look at establishing the safe concentration first, then adding something like radiator lubricant or water miscible cutting fluid concentrate to get some protection for the steel.
I used Butch's for several years, but currently use Boretech Eliminator. Eliminator has no ammonia. It has no noticeable odor at all to my aging nose. It's water-based and attacks copper so fast it leaves ammonia in the dust. I can't use brass jags with it because it attacks them so fast they color the patches, so I can't tell when the copper is gone form the bore. It also attacks the tin in leading to help break it down, though that is slow. The package doesn't say what the chemistry is, though I expect it may be a chelating chemistry of some kind.
As to the need for cleaning, that varies with the bore. When I got my first Garand from the old DCM, it came with a thick layer of well-oxidized copper visible from the muzzle. The WWII era military bore cleaner did not remove copper, so it's obvious the military didn't worry about it, but this gun would just build up too much. Starting the 50 round National Match Course with the bore clean, it worked fine until about the last 10 rounds of slow fire at 600 yards. Right in the middle of that last 20 round slow fire string, every time, the group would open up dropping two to three times as many points in the last 10 as it did in the first. It would take hours of repeated 15 minutes rests between patches wet with Sweet's to get the copper out, then the next day it would do the same thing over again. 40 rounds was its limit before the copper got too thick for it to shoot straight. That barrel just needed more cleaning than the match schedule would allow. So, I went to moly bullets in it some time in the early 90's. Then it would last over 80 rounds with no problem. Moly is probably what the old cupro-nickel bullets needed.
In the end, I firelapped that M1's old military barrel before I completely shot it out. Then it needed neither moly nor frequent cleaning.
