I don't think coyotes are cannibals, but here is what I witnessed. 2 years ago during deer season 5 coyotes came along the edge of field where my deer stand was located. I shot the first one and it went into a "spin cycle" the other 4 jumped on it snapping and snarling. I shot 2 more before the other 2 ran off. I have shot quite a few coyotes, all of them onesy- twoseys, but this was my first encounter with a pack of them.
I have shot coyotes with a 222 and 50 grain v-max out to 400 yards. They weren't DRT, but they either went into the spin cycle and died or only ran like another 25 yards and died. In my estimation, the 223 would be plenty adequate at 400 yards. From the videos I have seen prairie dog shooting and turning those guys inside out, terminal performance on a coyote should be adequate.