Yeah it gets hard to find data for heavy bullets in the 41. I'd try the Cast Performance Bullets website and Beartooth Bullets web site. I think you'll find data for 255 to 265 gr cast bullets. Since your bullets are SWC, you might have more bullet touching the barrel than some of the LBT style bullets so I'd start at the low end of the recommended loads and work up carefully. Alliant 2400 would probably be a good powder to start with.
You might try the Alliant, Accurate, and Hodgdon powder web sites or check out Steve Ricardelli's site too. Steve hangs out on GB here maybe he can help. [for give my spelling]
