I'd say that the varmint grenade would be well worth a try. I'll bet that the innards will be moosh with no exit.
Be careful betting money on it.
With a head on shot, I agree. On a broadside shot, it'll exit...and leave a large exit hole. There's only about 4" of flesh to stop that bullet on a broadside coyote, and there's just to much weight, even with the lightest bullets available in .243.
That small entrance/no exit is what I get with a 25 grain Berger Match bullet from my .17 Rem at 3800 fps. Even 30 grain bullets in that caliber will tend to exit, so a 55 grain .243 bullet at the same velocity is almost guaranteed.
For a fragile 35-40 grain .22 caliber bullet to not exit a broadside coyote most of the time, it needs to be slowed down to about .22 mag or .22 hornet velocities, depending on the bullet and load. Even lighter bullets in a .223 will exit much of the time at closer distances.
Most coyotes just don't have enough mass on a broadside shot to stop a 55 grain or heavier bullet, even at lower velocities. Higher velocities will make the bullet come apart easier, but the coyote still won't stop the blowout type exit wounds.
Believe me, I wish a good, fur friendly bullet existed for the .243. It's one of my favorite cartridges (I haven't been without a .243 since 1976 when I was 10 years old).
So, a person is better off to plan on an exit, and try to keep it as small as possible. Lighter bullets, if shot at velocities that don't cause fragmentation, have done decent for me. Bigger bullets can do the same thing, but make a bigger mess if large bones are hit (or, that's been my experience).
For a serious fur rifle, I generally recommend a small bore centerfire; preferably a .17 something or other (not a rimfire). About all a person can do with the bigger caliber rifles is ask questions, try some different things, and use what seems to work best; oh, and keep a glove-needle and some fishing line handy for sewing up holes.
It's just he nature of the beast.
Daryl