Of course if both penetrate completely through the animal, then the wound channel is the same volume, although I would suggest the animal would still react differently to a 400 FPE impact than a 100 FPE impact.... I know shooting a Grouse is more effective in anchoring it with an 18 gr. pellet than a 14 gr. at the same velocity and caliber, even though both give complete pass-throughs.... Also, a .25 cal pellet will anchor a Marmot far better than a .22 cal of the same FPE....
I am just curious here but what about the smaller calibers like .30 and up and just go for a head shot instead of having to worry about making a big enough wound channel and collapsing lungs and blood loss and maybe hitting the heart. II don't have any big bore experience hunting or otherwise. I have seen deer taken with .22 and .25 and .30 caliber powder burners without any problems with heart lung shots. So theoretically a .25 or .30 air rifle should drop a deer within 40yds with a headshot no problem right? I just don't have the deer hunting experience. (friends shot the deer I mentioned with the small caliber powder burners.) I am just trying to learn more about larger game as I work my way through the ranks of air gun hunting.