0-12fpe is .177 only
12-16fpe is .177, .20, or .22 with the nod to .20 and .22.
+16fpe is .22 or larger.
I’ve read through this entire thread, and this is the statement I agree with the most
(from a hunters perspective).
I have a .177 12FPE that shoots a 8.44gr pellet at about 813fps. It’s a little laser beam out to 90 or 100yards, but that little 8.44gr pellet just zips through a rabbits head even at 60yards. Over penetration is a real problem with .177’s even at 12FPE (at the muzzle), so I really can’t see any benefit to having MORE then 12FPE in a .177, because you are not going to be using a .177 to shoot animals much bigger than rabbits.
I owned a .20cal which was about 18FPE (sadly don’t have it any more) beautiful blend of .177 speed/flat trajectory and .22 heavier hitting power. Wish I still had it.
A .22 at 12FPE is doing around 560fps, which is a little slow for hunting things bigger then rabbits (personal opinion).
A rifle I currently use a lot is a .22 25FPE, it hits hard all the way up to possum and feral cat size animals and I use it on everything down to rats and mice.
So I agree with EquivelantDelta and the OP, and I feel the best way to pair a gun with its caliber, should be to match its power to a caliber.