I think the Jap A5 barrels are steel rated and they accept choke tubes. Jap barrels can be had, though no A5 barrel is inexpensive. Jap barrels are chunkier than Belgian barrels and sometimes it's necessary to relieve the forearm inside a little bit to allow it to fit.

Every normal man must be tempted, at times, to spit on his hands, hoist the black flag, and begin slitting throats.