If Nerf Hyper rounds are 13-14mm diameter, then it stands to reason that with minor modifications the Sportsman would be able to fire them. With a massive hopper it may make for
Amazon.com: Nerf Hyper Bundle, Siege-50 Pump-Action Blaster, 65 Nerf Hyper Rounds, Up to 110 FPS Velocity, Eyewear (Amazon Exclusive) : Toys & Games
Nerf Hyper Rush-40, Siege-50 and Mach-100 review: where the rubber meets the foam - The Verge