plain white vinegar works just as well, for the breech plug.
Bingo, give the man his prize!!!!
For many years i've used Windex with vinegar, now called Multi-Purpose Windex. Just spray it on and you can watch see the crud disappear. The more stubborn stuff can be removed with a toothbrush. It takes me two minutes to clean a breechplug.
Not sure if it works on crud left from BlackHorn. It works with the crud left after firing BP the other substitutes. The crud left after firing BP, Pyrodex, 777, APP, JSG, Black Mag, and Pinnacle all contains a base. An acid will destroy a base.
Before leaving the range my guns get bore swabbed using a patch wet with Windex with vinegar. Speeds up the cleaning at home.