Hi, yesterdaysyouth and guys,
True some people use Hoppe's on nickel plated guns with no problem. Ammonia can attack nickel, but much more slowly than copper, so if the nickel does not reach the copper, everything seems OK.
But if there is anywhere (muzzle, front of cylinder, sideplate joint, screw hole) that the nickel may be cracked or chipped, the ammonial cleaner will eventually get to it.
I recommend using a non-ammonia cleaner. Why take chances?
Jim