“Shotguns have no rifling and any thing with a barrel length under 19 inches is verboten.”
18 inches is the minimum legal length without going into NFA territory. Sheesh. Every body is an expert.
I was told 18 too, but a guy I know who bulged the barrel on a 12 ga and wanted to cut it down was told 18 1/4, 18 1/2 by various agencies, I think the local Sheriff gave him the 18.5. I told him its a good gun I would rebarrel it which I think he wound up doing.