You might try an "Undertaker" choke. They're relatively inexpensive compared to most turkey chokes and often really improve the performance.
If you decide to step up and spend a little, try Clark's "Swarm
" choke. I use it on my daugter and wife's 20 gauge turkey guns. It's amazing how much difference the Swarm
choke made in the pattern.
You can pick up a Swarm
, Clark's site. I've shot every brand of ammo I can think of through the Swarm choke and it gives me an evenly-distributed, round pattern at 40 yards regardless of the brand of ammo. Clark developed the Swarm
to shoot Hevi-13
(he'll correct me if I'm wrong). My daughter and wife use the Hevi-13, #6s, and I swear a fly couldn't make it through that swarm of #6s at 40 yards! A turkey doesn't stand a chance.