On Jackson's sight, the speed calculator asks for SE/PDF ratio. A small change has a big affect. Other than a bow report, is there any way to find this out? What is virtual mass? Is there any rule of thumb as to bow efficiency? I have a Bear Vapor 300 set @ 55# w/ 30" draw. Any help is appreciated. I'm trying to decide on what broadhead to use, though I intend to test several different ones this summer. I'm leaning towards 125 grain heads. My bow's speed will enter into the final decisions. Thanks.


Phil.