These SureShell shotshell carriers for the Mossberg 500 and 590 feature mounting brackets with integral top Picatinny sight rails. The brackets are secured to the weapon using the top mounting screw holes found on Mossberg 500 and 590 shotguns made since 1997. The SureShell shotshell carriers are thus slung on the left side of the receiver, securely fastened at the top. No other shell carrier mounting method is as secure or looks as good.The 20 inch rails are anchored at the front by a magazine clamp that features a short length of Picatinny accessory rail at the bottom.