Energy is calculated not measured. Momentum can be measured or calculated.
If you think that a FMJ solid 458 would not be lethal in your Deer story think again. A bullet strike is an inelastic collison, momentum is transfered in all collisions. Energy is transformed into other forms of energy in inelastic collisions ie thermal, sound, etc. Energy is transfered in lastic collisions as well as momentun.
The dynamics of wound trauma incapacitation are much more complex than a simple energy calculation. Tissue is crushed by the bullet as it passes thru, the faster a bullet impacts the more hydraulic presure that is created, if this pressure is grate enough it can also add to the wound channels size.
A 22-250 bullet at 3600 FPS has 1583 FPS. a 45 caliber bullet at 1400 FPS has 1567 FPS. Are the 2 equal in effectiveness on a Bear or a Buffalo? Of course not FPE is a useless number written on a piece of paper with no real value in acertaining the wound trauma of a cartridge
