Check the listing for details. 12ga to 10mm Shotgun Adapter - Chamber Reducer 18" Long. Condition: New. Listed at 119.10 USD. 12ga to 10mm Shotgun AdaptersLength: 18" 10mm Shotgun Adapters Allow a 12 Gauge Break Action Shotgun to use 10mm ammo. For 3″ as well as 2.75″ ChambersCompatible with Break Action single as well as double barrel shotgun.Comes with multiple O-ring configurations. As a result, easily achieving a good fit for 12 gauge shotguns.Finger Grooves for easy extraction of spent casings.Black Oxide coating as a result provides notably better corrosion protection (for maximum corrosion protection keep a thin coat of oil on the insert)Rifle dimensions are .390″/.400″ with 6 grooves and .120″ wide with a 1:14 twist rate. 1-14 twist rate.*Should only be used in capable shotguns with SB1 or SB2 or equivalent receivers. Made in the USA If you're not happy with the product for any reason send it back within 30 days and I will refund your money.