Couple of reloading questions?

[Johnny reb]

Any one have any experience reloading the 300 rcm. And what powders are you having luck using? I'm also working up loads for a 8 mm rem mag and I've got a good load using 200 grain noslers getting 1/2 in groups just got some 220 grain sierras and having trouble finding good powder combination for it. All suggestions are greatly appreciated