Slugs or shot?
With full choke and buckshot, roughly 70% of the shot (~6 pellets of 00) will be within a 30 inch circle at 40 yards. A coyote profile is smaller than a 30 inch circle, so assume you get half the shot (~3 pellets of 00) into the animal and that half of that shot is not in vitals, so you end up with maybe 18% of shot (~1-2 pellets of 00) potentially hitting vitals at 40 yards. That does not bode well for a single shot kill at 40 yards, but is probably the maximum effective range.
Open up the choke and the effective range drops fast.
You might want to consider shorter shots, like 24-30 yards, or go to a slug to considerably extend your range.
Coyotes are fast and smart. Getting into position and getting a shot at 40 yards will require some stealth on your part.
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