Brouahah and I were shooting one day and he commented on how loud my BH red box was that I was shooting. I didnt notice. Then I listen closely to alternating rounds of the blue box we had and red box. Sure enough one went bang. and one went BANG! Shot both through his chrono and the red box was about 160 fps faster than the blue for an identical load. A call to BH determined that this was a too hot batch of redbox and we sent the rest in for disposal and got several boxes to replace what we sent in. In that case the feel and noise led us to the chrono but ony the chrono will tell you for sure. Perhaps the bullets are not quite 55 grains and one is a lil high the other a lil low, perhaps its the burn rate of two different powders, etc. The higher velocity ammo chronos a higher velocity. Sure the sound and recoil can give you a hypothesis but it needs to be PROVEN to make any claims.