Nerf - Zombie Strike Hammershot Ultimate Upgrade Nerf - Rebelle Sweet Revenge Ultimate Upgrade Upgrade your Nerf Hammershot to the best possible performance using this spring compression spacer and a secondary Upgraded 8kg Retaliator spring Upgraded Retaliator 8Kg spring: http://modworks.blogspot.com/2012/07/nerf-n-strike-elite-retaliator-mod-guide.html Other modifications can be found at Better Nerf By Science: http://nerfscience.blogspot.com/2013/09/the-works-guide-zombie-strike-hammershot.html .03 layer, 30% infill To use just as a spacer or upgrade to a secondary stock Retaliator spring I recommend one of the files that have the word "Stock" in the name such as: Hammershot_Maverick-Stock.stl Hammershot_Maverick-Stock-v2.stl if you want the highest performance I recommend a secondary 8Kg Retaliator Spring and the file with "8Kg" in the name such as: Hammershot_Maverick-8Kg.stl Hammershot_Maverick-8Kg_v2.stl Using both the Stock Hammershot Spring and the 8kg Retaliator spring at the same time plus the Spacer the gun is still primable with one hand. I personally use the original version of the files and don't have any problems but some people have mentioned that the spacer will grind along the inner shell's seat-post housings during priming and releasing of the spring so I created the "v2" The best source for the Hammershot upgrade is found: http://nerfscience.blogspot.com/2013/09/the-works-guide-zombie-strike-hammershot.html and the Upgraded 8Kg Retaliator Spring: http://modworks.blogspot.com/2012/07/nerf-n-strike-elite-retaliator-mod-guide.html