I don't have any experience with the 416 Remington (in my view the most sensible of all the 416s), but I've used both UMR and H4350 in my Rigby with great success, then again those larger bores are very forgiving.
A good principle to guide me through life: “This is all I have come to expect, standard lackluster performance. Trust nothing, believe no one and realize it will only get worse…”
