Without digging through my old files, the suggestions of 79 to 84 worked for me with RL-15 and it was my chosen powder hands down..
I recall that my favorite load was a 400 gr. or 450 gr bullet at 2300 to 2400 FPS was my chosen load, and I had some leeway between guns, but this load of 12400 worked in all the 416s I owned over the years and it killed well..I never saw the need for more velocity than 2400 FPS, although I could get more velocity when working up loads, but bullet performance on Buffalo etc always seemed perfect at 2400 FPS. so I stuck with that.