My 336 is noticeably more accurate with the Hornady Leverevolution factory ammo than the Remington CoreLokt. Assuming the same is true for your brother's rifle, I would try to replicate the factory loads. You can buy Leverevolution powder and you already have the appropriate bullets. By reputation, Leverevolution powder performs best with compressed loads. I would start with this powder at the recommended minimum and work your way up until you have the best accuracy. If we are talking about deer as a target, any load you put together that is the most accurate will put deer on the ground handily, so there is no point in pushing for an extra 50 or 100 FPS if it means giving up accuracy.