This cast steel adapter enables the use of any 12 gauge Remington 870 stock. There are many more options for the 12 gauge than 20 gauge” including Mesa Tactical’s Urbino Stocks” telescoping stock adapter kits and even the Hydraulic Buffer system.
Mesa Tactical Lucy Stock Adapter, Fits Remington 870 12 Gauge, 20 Gauge to 12 Gauge Stock Adapter, Black 93890
