The Beretta 1301 extension increases magazine capacity to 7 rounds (capacity determined with 2 3/4" shells and may vary with shells of differing length). Barrel clamp kit includes 1301 Tactical-exclusive clamp, Picatinny rail, and QDA swivel attachment.Features :Spare Generic Spring Included,Increases Magazine Capacity to 7 rounds with 2-3/4" Shells,QD Sling Attachment