Ditto the eye relief. It's usually best to mount your scope either on the barrel or on a cantilever from the barrel. Receiver mounted scopes don't fair as well because most shotgun barrels (pretty much anything with interchangable) move to much.
You are correct on the barrels moving, and the longer eye relief is sometimes needed when mounting to a cantiliever system.
but even then the barrel will twist some between shots. causing the point of aim to vary slightly.
I had an 870 with a 24" hastings rifled barrel on it pegged by a gunsmith, and you can't beleive what this and a trigger job did to the sizeo of the already impressive groups. Eveny though I still hunt in the rifle zone, I use this gun a lot, I would have no problem taking a 150 to 200 year shot witht he gun and had never killed a deer with a shotgun so I had this built.
Now they have the crossbow thing, and I guess I wll need to add one of those to my arsenal as well. Will the need for new toys never end
