There are 2 types of winning score usually... Closest pellet to the "bull" or "X" and most pellets on paper. If the first... then the cheap promo ammo my 2 local turkey shoots use... it is really a game of chance at the 95 feet we shoot.
If the second, the guys will use real tight chokes to win. My best advice is to see if they will tell you what ammo they have bought and ask to come early to shoot the same ammo you buy in your gun to practice... One of our turkey shoot hosts is a hunt club and will let us show up early to practice.