They're a rifle barrel, with an OD/fitting that fits a particular shotgun gauge, locating itself centrally in the smoothbore barrel, internally chambered, bored & rifled for whatever metallic cartridge.
The insert has an extractor that aligns & piggybacks on the shotgun's extractor/ejector, following whatever it does.
They are strong enough, on their own, to contain the pressures of the metallic cartridges Krieghoff offers, letting the shotgun barrel(s) serve only as a carrier(s).
Of course, it's up to the shotgun owner to devise some sort of sighting method.................
They additionally operate very effectively on a buyer's wallet...........
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