S&J Hardware Magazine Extension for Mossberg 590A1 Shotgun A review of the S&J Hardware Magazine Extension for Mossberg 590A1 Shotgun. Share this gun video:Click to share on Facebook (Opens in new window)Click to share on Twitter (Opens in new window)Click to share on Pinterest (Opens in new window)Click to share on LinkedIn (Opens in new window)Click to share on Tumblr (Opens in new window)