First what shotgun do you have? Then as Sheridan said the constriction is the numbers if you are a numbers guy- wikipedia has a nice firearms choke page that explains it better.

There are a lot of great chokes to tighten the pattern and extend the effective range of killing a turkey. The best approach is get a bunch of choles and different shells and find out what works best for your gun. Now that isn't always cost effective. Find one and then pattern with a few difefrent shells- winchester, rems or federal- some like heavy shot too. Shot at 20 and 40 at least and the one that puts the most bb's in the kill zone is there choke and shells you'd like. Shells and chokes react different in each gun. What is perfect for mine may be aweful for yours.