Re: Can a shotgun choke be too much?
A gun can absolutely be over-choked.
But there's no hard & fast rule as to when it will occur. There's some pretty universal guidelines. But EVERY gun/tube/load combo must be proven or disproven at the patterning board. Some combos that make all the sense in the world just plain won't pattern. Some combos that have "failure" written all over them turn out to be monsters.
Case in point: Several years ago, I spent countless hours and fattened cheekbones trying to get a coarse lead load to pattern well in a BPS 10 ga. for coyote duty. #4 buck, BB and #2 shot failed to give any patterns worth a hoot through a 1/2 dozen or more tubes that should have been just right. As a last ditch effort, I screwed in a XXX-Full Comp-N-Choke tube (the manufacturer even reccommends shot #5 or finer) and ran 2 1/4 oz. of #2 shot through it. It was MONSTROUS !!! The combination should have been, by all calculations, WAAAAY over-choked and should have produced much deformed shot and many fliers. But ti didn't.
As a generalization, for turkey, your Mossy 500 should like some combo of a 3" #5 or #6 shot through a tube in the .650"-.660" range. But only time spent with big paper will tell the real tale.