Killbambidead has given you good advice. You don't have to shoot 3.5 inch shells, but get a gun capable of it.
Check your regulations concerning shot size. The lower the number the larger the pellet. So a 3 inch shell with 1.25 ounce #6 shot will have more pellets than the same shell with #4 shot. Practice with different brands, get a good turkey choke and see which one your gun patterns the best.
I like Mossberg shotguns for a good combination of durablity and price, but their are many good brands (Benelli, Remington, etc.) I have a Mossberg 835(pump). The 935 is semi-auto.
Like bows in archery, you need to find one that feels good to you.
"Doing the best I can....AT ALL TIMES!"
02 Mighty Mite 27'' 72lbs
Beman Matrix 468gr. 255fps
04 Protec 27.5'' 70lbs
GT Pro22 349gr. 260fps