This spring is now included in the Hornet MK5 kit. R9-HW77-97
With its new design it makes full power but is more docile than stouter springs. Works great with the drop in Hornet seals and even correctly sized factory seals.
Fits Mksmn 55-70 break barrels as well. HW 85,95,77,97,60,61, R9,10,11 etc.