When I said I shot 10 squirrels with my 32 fpe 22 caliber PCP and they were DRT I didn't mean they took a step or two or moved after the shot. I mean DRT. Head shot squirrels will sometimes flip around some and a few might have done that, I don't keep track of it. But when they are flipping around they are still dead. Nerves are just triggering spastic movement. The one today just slumped and fell. It was just over 30 yards away.
I shot two squirrels with the exact same placement last year. One was with my 32 fpe 22. The other was with a 19 fpe 177. The 177 shot squirrel took a step or two and dropped. The 22 shot squirrel dropped immediately. Placement was behind the near side front leg and out the front of the chest near the other front leg. I don't think the 177 exited but the 22 did. These shots were about 20 yards.
I don't care if you guys want to use 357s on squirrels, I am just pointing out it is more fpe than really necessary. I'm not a fan of low teens fpe or less. I think high teens (like 18-19 fpe) work well out to 30 yards or so. 30-40 fpe work great as far away as you can put the pellet in the right place. More than that might be fun but it isn't really necessary.
With respect to higher energy projectiles not exiting that is due to expansion. I test expansion in wet paper. Metalmags expand at even the low velocity my Prod gives them. They also penetrate less due to the expansion. The greater the expansion, the less the penetration. May be handy if you are worried about hitting something after the projectile passes through. Penetration could be cut in half by significant expansion. That might be good if you are using a 357 on a squirrel but not if you want to eat it.