I don't regularly hunt pheasants now, but most of the hunting I did when I had the chance was with a 20ga O/U Browning fixed M/F... Killed them very dead, used Remington copper plated #6s or Fiocci Golden Pheasant (nickel plated).
A couple boxes lasted several seasons.
I preferred the 6s for load density over the 5s and was using tight chokes. With good dogs shots are not long usually.
