these are shotgun adapters aka chamber reducers aka shotgun inserts and called by a few other names. they allow you to fire lower gauge (caliber) shotgun shells out of a larger bore
Rifled Shotgun Adapters - Gunadapters.com
X-CALIBER Survival-Rifle Gauge Adapter System - Soldier Systems Daily
Adapter
7.62x39 Shotgun Adapters - Shotgun Adapters - https://chaszel.com
12GA to 9MM RIFLED Shotgun Adapter - Chamber Reducer - Stainless - Free Shipping | eBay
Sterling, 7.62x39mm, 123 Grain, Steel Casing, Case of 1000 Rounds UPC: 8698779967604 - Global Ordnance
BARRELETTE- MINIATURE TRAP/SKEET 22 CAL BARREL INSERTS 20 GA for sale
The Shooters Box case and ammunition reloading gauge.
X-CALIBER Survival-Rifle Gauge Adapter System - Soldier Systems Daily
Is the 7.62x39 the same as a .308? - Quora
Caliber conversion sleeve - Wikipedia
With Battery Tactical 12GA 20GA .223 7.62x54 7.62x39 9mm Cartridge Red Laser Bore Boresighter For Pistol Rifle Collimator - AliExpress
7.62x39 AK-47 Steel Shells Once Fired Casings – EmptyShotgunShells.com
Mili 12 Gauge #00 Buck Shot 3.0" 9 oz. 1350 FPS
7.62x39 12 gauge barrel adapter warning! - YouTube
Camber Adapters, Survival tool? Or just a gimmick? | Gun and Game Forum
X-CALIBER Survival-Rifle Gauge Adapter System - Soldier Systems Daily
7.62x39 124gr FMJ, Brass, 20 Rounds, GECO
Chamber Adapter - Don't Bother | Bushcraft USA Forums
7.62x39 Shotgun Adapters - Shotgun Adapters - https://chaszel.com
