+1, RL-22 for the .300 Win Mag. It would have to be on the short list of best powders for that caliber.

Both the .300 Win Mag and the .308 Win was very forgiving and easy calibers for which to develop good loads. I try to not have multiples of one caliber for the reason mentioned. With loads and brass specific for each gun, having several in a caliber is just like having different calibers.

BTW, H4895 with 150 gr. bullets was the tack driving load for my .308.