Jim, if you have the 590S Shockwave, you do not need an adapter. If you have the original 590 Shockwave, you need the OpSol mini clip in order for the shells to cycle properly. You don't actually need it to shoot the mini shells, just for the gun to cycle them, without it you would need to load them in the chamber one at a time. budsgunshop.com/product_info.php/products_id/36595/opsol+texas+miniclip+mini-clip+for+mossberg+500+590+12+gauge+1+round+polymer+black+finish .....Have a great day!

The opsol adapter you want is available at the link below. It will help cycle the mini shells.
budsgunshop.com/product_info.php/products_id/36595/opsol+texas+miniclip+mini-clip+for+mossberg+500+590+12+gauge+1+round+polymer+black+finish

some will without the adapter I would try an see if it works. if not you can get the adapter here budsgunshop.com/product_info.php/products_id/36595/opsol+texas+miniclip+mini-clip+for+mossberg+500+590+12+gauge+1+round+polymer+black+finish

Jim, the shockwave will shoot them but won't cycle short shells properly without an adapter. Buds has one in stock that'll work and is relatively inexpensive. Here's a link to it if interested. Hope this helps, link here................ budsgunshop.com/product_info.php/products_id/36595/opsol+texas+miniclip+mini-clip+for+mossberg+500+590+12+gauge+1+round+polymer+black+finish

Hi Jim, yes and Buds has you covered Sir : budsgunshop.com/product_info.php/products_id/36595/opsol+texas+miniclip+mini-clip+for+mossberg+500+590+12+gauge+1+round+polymer+black+finish