The etching with ammonia based cleaners only occurs if you let it dry out on the metal, if kept wet there should be no etching.
Yes not advisable to let ammonia solutions dry.
but also true -
Ammonia solution can be used to etch steels.
How well 5% in Sweets or less in other bore
cleaners can etch steel, is another matter.
Loading manuals from the 50s, recommended
26% ammonia for at least 20 minutes in a
plugged(sealed) barrel , then a good flush,
dry and oiling.
Ammonia is also hydrophilic
, meaning it
draws moisture from the atmosphere.
I still use Sweets responsibly without a worry.