Hi Jim and welcome. Unfortunately, until another aftermarket company make higher capacity magazines, 3rd Factory Magazines are it currently : budsgunshop.com/product_info.php/products_id/27185/ruger+90633+american+rifle+450+bushmaster+3+rd+black+finish --- Cheers and stay safe!

Hi Jim, unfortunately no. This is a proprietary magazine. There was an outfit called Lucky 13 in Australia who made ten round mags for this gun, but they are no longer in business.
Stay safe & have a great day!

Unfortunately thats a no, Ruger has its own proprietary 3 round magazine.

no the Ruger ranch has its own style mag and is only available in 3 rounds extra factory mags here budsgunshop.com/product_info.php/products_id/27185/ruger+90633+american+rifle+450+bushmaster+3+rd+black+finish