Regarding the tie. If someone breaks and arm and you've no necktie what are you going to use as a temporary sling? If some one breaks a leg two stout branches with two jackets and a couple of neckties make a stretcher. Or as a temporary tourniquet if a vein or artery is severed. It's the same reason stocks are worn when hunting. Tradition because the thing has a use other that as a neck garment. I don't like wearing a tie either when shooting anything as it restricts the turn of the head. But I will on a day out in the field with others just case it's needed for that second purpose.
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As for a self-loader by date of invention Browning's Auto-5 predates the modern O/U by nearly a decade. Designed in 1900 it's another nine years until Boss's O/U comes to the market. I'd have no issue personally with using one on a formal day and, to my mind, it's all nice blue steel and walnut at least it won't have God awful multicoloured choke tubes sticking visibly out of the muzzles. Still horses for courses and if it upsets others it stays at home for their enjoyment of the day is also my enjoyment.