Can someone explain this relationship between energy ft. lbs and recoil? I'm trying to decide on a defense load for my 357 revolvers. Critical Defense is listed as a low recoil round but has 624 ft lbs. Critical Duty is listed as more powerful and penetrating but less energy at 487 ft. lbs. How can this be? Is there an other component to this formula I'm missing like pressure? I would think the higher the ft lbs the more felt recoil in the same gun. I'm a bit recoil sensitive I guess.
Power and Energy are 2 different things, so it's possible one factor can be more and the other less.
The differentiator is Time.
Energy = Power x Time.
As to penetration, if one bullet A is more aerodynamic (and hydrodynamic hitting a water based target) than another bullet B, then A may penetrate further than B into the target.
As to the recoil, most revolvers don't have muzzle brakes and have no recoil mitigation mechanisms as some semi handgun (and rifles do). So the shooter is going to feel the full recoil as a fairly sharp pulse containing all the energy over a one to a few milliseconds. Heavier revolvers take longer to put in motion from the recoil force, so a proportional increase in time. The heavier the revolver, the slower the recoil.
A semi-spreads that out even more as multiple movements / actions are involved, so the felt recoil is less even though the muzzle energy might be the same.
Here's a slo mo of those reactions on a semi-rifle:
12,000 ft-lbs of bullet (and recoil) energy in (almost) slow motion. The bullet exits the barrel before any appreciable movement in the weapon. Then the barrel starts moving back against 2 stout springs. This action is followed by the bolt carrier moving back against a single large spring (similar to an AR-15). Just after that you can see the shooter starting to feel the delay and spread out recoil.
The 12,000 ft lbs of energy 'felt' by the shooter is the same amount of energy felt by a target at pointblank range that fully absorbs the bullet energy..... except the shooter feels it spread out over about 1/4 second, where the target is absorbing the energy in well under 1 millisecond.
So you might be recoil sensitive to 'sharp' (fast) recoil, but less so to recoil that is more of a 'push' as seen in this video.
Does that help any?
(P.S. The 12,000 ft lbs of recoil from the Barrett is effectively a push and much less unpleasant than the sharp 280 ft lbs from a Bersa .380.)