Larger amp; Wider contact area inside of BB pellet - Better Performance for Heavy BB pellet. - The #34;Shield #34; shape groove design has better hop effect when tensioner /lever press it. - Retain the steel #34;C-ring #34; design for airseal from #34;Transformer HOP #34;series- The R-hop Rubber kit begin from a small group user who want to increase the range and hop effect of heavy bb. - The title #34;R #34; mean the #34;RANGE #34; Recommended hardness / FPS combinations: - 50 degree: Up to 360 FPS - 60 degree: 295-390 FPS - 70 degree: 360-460 FPS - 75 degree: 425-490 FPS - 80 degree: 490 FPS up