if he doesnt want to dial i doubt he wants to reload which basically rules out 6.5wsm and 7wsm has fark all ammo available. 300wsm would have more drop and wind drift at 400m.
270wsm actually makes sense for what munsey is describing. Personally i would go 7rem mag tho as 270's are gay and the 7 rem mag will be basically the same in drop and drift at 400m then slightly sneak ahead the further out you get.
All magnums will have about the same amount of drop and drift at those ranges. But the 270wsm may have the least.... wiithout actually doing any numbers
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