I think that, realistically, you have to consider the ballistics of the bullet you are shooting from your 223.
The 223 was the first cartridge I reloaded. I am no guru on the cartridge but I did shoot a lot of them that I hand loaded from a single shot ruger.
I created two loads, one using a 40 grain vmax and the other using a 50 grain vmax.
The point blank range on these, meaning one inch high at 100 yards and 1 inch low where it hit was between 225 and 235 yards.
Beyond 235 yards the bullet really falls off. So if you are shooting at something 300 yards out the bullet is going to drop about 45 inches or so from its highest trajectory. The heavier the bullet, the greater the arc.
If you could actually hit something at 400 yards I am sure it would probably die. But the arc you would make with the bullet would make hitting something unlikely on the first try. Not that it can't be done, but coyotes don't wait around, you get one shot, maybe two and its over.
But if you get your rifle dialed in at its point blank range with the round you are using then you will know the maximum distance you can shoot out to.