I've been using my .20-250 exclusively for calling Coyotes for the last 5 years, love it.
Here is a picture from a Predator club I belong to, tallying up "proof of kills" for this season.
85% of those where killed with my .20-250, with a 40 grain NBT.
Since my last post, I've re-barreled it. The 12 twist Lilja wasn't cutting it, wouldn't shoot and also fouled badly. Replaced it with a 11 twist Krieger, much better now!
The Smith who built mine (Greg at Gre'Tan rifles) has a .20-250 set up for 55 grain Berger's for sniping Coyote's. I know he whacked one in the neighborhood of 700 yards this season. He would be happy to give you the low down.