I actually added about 10oz of weight because I like the swing of a heavier gun. I had purchased a recoil spring with -25% tension and it didn't work with the added weight. I put the factory spring back in and removed the wieght and it worked fine. I lowered the wieght to 6oz with the factory spring and it cycled, but did hang up some. I'm thinking about trying it with the 6oz wieght and the -25% spring. Any thoughts?