.223 Shooter,
You did not mention the ammo you were using on that coyote that took all the hits in the chest. That's a VERY big point. My guess is that you were using .22 LR solids and I can you from past experience, those are NOT good stoppers on fox squirrels, let alone something the size of a coyote. I do NOT believe, for a second, that ANY coyote would take the number of chest shots you mentioned from a regular .22 LR hollowpoint, let alone a .22 hyper-velocity long rifle. WHAT you hit that 'yote with (load-wise) makes a HUGE difference and I think you should have mentioned it.
On that same note, my brother DID hit a coyote with 3 subsonic (Eley) hollowpoints in the lungs and the 'yote did get away. I KNOW they can take a real punch but had those been Stingers or Velocitors at the 30 yards or so that he shot the critter, that 'yote would have very quickly become a good 'yote.
I have also read posts where a .223 IN THE CHEST failed. What the writers NEVER mention though is how did the bullet PERFORM! Obviously, if the bullet does NOT perform (and that CAN happen in any caliber no matter how rare), then that can NOT be held against the cartridge. Otherwise, we'd all be shooting .375's for coyote UNTIL someone in time has a bad experience with it!
Sorry for the rant.