I think you should limit your shots to under 40 yds, terminal energy is not very high beyond that distance. If you shoot out to 50 yds the most likely results will be a wounded turkey or just a miss.
I have heard that the federal Hevi-Shot, I think, one of the new alloy shotshells, is rated out to 45-50 yds. I don't use it for two reasons, the first is cost, the stuff is around $20.00 a box and the second is that calling a tom in close is what spring turkey is all about for me. YMMV