I just bought a dozen 400 3d Cheetah's at 28" to try for 3D season. I've been shooting Carbon Express Maxima 3D 250's at 28" & wanted to try a little bit lighter shaft. Problem is they weight is only 10 grains different. How is this possible when the cheetah's are "suppose" to be 6.4 gpi & the maxima's are 7.3 gpi? I have the standard nock and insert in the cheetah's & the standard collar & nock and screw in insert in the maxima's. Anybody got an answer? I was hoping to be able to shoot 4" vanes on the cheetah's and lose the 4" feathers on the maxima's and be right around the same final weight because of the 25 grains I thought I was losing going to the cheetah's. Thanks for any thoughts.