action army hop up bucking fit with marui vsr10 /g-spec, jg bar10, hfc vsr11 made in taiwan action army this hop up bucking is a great upgrade to ensure a better air seal and proper backspin on the bb during flight. the material used on this hop bucking is called "hnbr". here is a short description on hnbr, hydrogenated nitrile rubber (hnbr) is a viable alternative to polychloroprene for many automotive applications such as timing belts, seals and hoses. it has excellent mechanical, thermo-oxidative and chemical resistant properties and an excellent operating temperature range. fit with marui vsr10/g-spec,jg bar10,hfc vsr11,marui pistol, socom gear r700