The longer you hunt them the less you need....
When I first started I had a flock of decoys, every call you could think of, 3 1/2 in nitro shells guaranteed to knock um down at 70 paces, turkey vest, and although I hate to admit it I did something I never thought I would do and tried a red dot scope....on a shotgun lol.
The scope lasted until the man who taught me to hunt turkeys looked at me like I was nuts, the decoys have been long gone, shedded the vest a few years back along with the 3 1/2 in shell. The past few years we have gotten close enough to grab on a couple of occasions but I will probably keep the 3 in shell anyway just because it patterns well in my gun.
But the answer to your question is, if you killing birds within 40 yards you don't have to have a 3 1/2 in shell to do that with.
My Brother: WMB