A .243 would be my choice for coyotes in an AR10 platform.
But for coyotes, I much prefer an AR15 in .223 with V-Max bullets. It's hard to beat on killing coyotes. In fact, I think it kills coyotes better than most .243 applications. And you can load/buy ammo cheaper.
I'm setting up a night vision AR10 now. But mostly for hogs with coyotes as a secondary target. I'm setting up an 18" .308.
.243's are pretty loud as it is. I sure wouldn't like shooting any shorter than an 18", and would really want a 20" more.
