I blew a leg off a big red fox one time with the 25 grain Hornady HP, but other than that I have found the .17 Rem to be very fur friendly. I have no idea how many coyotes/fox/rock chucks/bunnies/turkeys have been killed by that bone stock BDL .17 Rem of mine.

I use CCI 400s and 23.5 gr of IMR 4895. I have not experimented much (a very little bit with IMR 3031), and for good reason. Sub 1/2 inch groups don't need messed with.

I would caution though, the 20 grain VMAX can fail to penetrate a coyote's shoulder at 10 yards. The 25 grain HP and VMAX though, have been incredible coyote killers.

I don't have much experience with the fireball/Mach IV, but have not been disappointed with the vanilla Remington.
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She wears a Leupy 6x42 now