Lets figure out that FRE equation you provided.If we assume a limited gun weighing 38 oz, 180gr bullet at 175pf, we get 4.237 ft/lb.
Add 3oz onto the weight of the gun, and we get 3.927 ft/lb. That's a ~7.5% decrease in kinetic energy. That's only for a free recoiling firearm. ie, one that isn't being held.
Yes, the lighter gun will have more kinetic energy after a given distance traveled than the heavy gun, in the same way the lighter can has more kinetic energy than the heavy can at the same height.
But you're there to hold the gun, so the energy is transferred into you instead. We're still just changing the way the energy (recoil) is felt.
Not to mention, this is just calculating F.R.E. based on the total weight of the gun. So you had better hang your 12oz can of paint from the grip so the recoil is "less", it'll work better than the tungsten barrel.
Or:
If the recoil is "less" where did that energy go if not into your hands?
http://en.wikipedia.org/wiki/Conservation_of_energy
Seems to me that 3oz of additional mass decreased the rearward momentum by 0.31ft/lb before it was transferred into my hands by your calculations, thank's.