NE,head shots on called coyotes is great theory on paper,but does not work in the field.Coyotes are cagey(seems everytime they show their mug,someone shoots at them)Up here I use an AR-15 and I have dropped many drt,and many that ran two hundred yards then piled up,shot placement was in the sweet spot,coyotes are tough.I have also dropped a bunch with the .22-250 50 grain vmax. Dont think about the HMR for a calling gun,you will wound to many dogs.I think reading your post I think your concerned about bullets down range at night,(a very important concern)am I correct? If thats the case I would use a .223 with a light bullet or a scatter gun,up here at night the coyotes get agressive and come in close fast,and if your dickin around trying to get a head shot,they will be leavin faster!! Use a scatter gun...
ALL ANIMALS ARE EQUAL,BUT SOME ANIMALS ARE MORE EQUAL THAN OTHERS..