Very short bows will often have lower virtual mass figures. Tuomos bow was kind of exceptional with the speed he got. The short bows also store a lot less energy. The primary reason I liked to use virtual mass was to isolate hysteresis from vibration. Self bows will rarely, if ever, go along with virtual mass theory because the hysterisis caused by set is time sensitive and the faster the bow shoots the more the losses are from hysterisis. Glass bows on the other hand Will stick very close to VM projections but still trending slightly slower. I had an odd way of calculating stored energy and VM, most experts don't agree with it, but numbers seem to follow more reliable patterns. I would use an extremely heavy arrow to test the speed, maybe 2,000 grains, and then I would go to 1,000 grains, and then 500, 300, then 200. The 2,000 grains would almost always reflect about 95% efficiency so it was a good starting point. I no longer remember the exact process, but it was fairly simple, and I felt it gave me more useful information about the damage from set. Tuomos bow doesn't act like a bow with hysteresis. Isolating and identifying where losses in energy occur gives the bow maker more opportunity to improve.
