MadBull Airsoft red rubber hop-up bucking 60°(2pcs) The Shark bucking and Fishbone X Balancer were originally developed for the MadBull 470 CO2 powered drop in mechbox to prevent double feeding of BBs and to prevent BBs from rolling out of the barrel. By having 3 special "fins" inside the bucking, Shark Hopup Bucking can hold one and only one B.B. tightly in the chamber. In the mean time, to our surprise, we found that this bucking could enhance the velocity on some AEGs. Not all AEGs will have the same results and the result could be different from one AEG to another. Unfortunately, we don't know the exact reason because each AEG has its own characteristics. However, we do believe that the friction (from 3 fins) applied onto B.B. will increase and slightly build up the pressure behind the BB before it starts traveling down the barrel thus enhancing the velocity much like a blow gun, spit balls with a straw or similar concepts. The Fishbone X Balancer is designed to produce and even downward pressure across a greater surface area of the BB in order to less the chance of off axis back spin being induced from the hop p system with traditional round nubs. Why 60 Degree? 60 degree rubber is softer than normal 80-90 degree rubber. The softer rubber tends to create a good air seal with the nozzle Softer rubber provides higher friction/grip and makes the hop up effect more pronounced with less velocity loss associated with typical hop up systems where the hard bucking must be pressed deep and hard into the hop up relief cut on the barrel. This causes dramatic reduction in speed How to install: Apply some silicone oil inside and outside the bucking when installing onto the barrel and into hop up chamber. Tech Note: Hop-Up Buckings are wear items and should be changed as often as feasible. And should be replaced when upgrading or anytime the inner barrel is removed from the hop up unit. Small pin holes and tears can occur when removing and reinstating used buckings. Reference: