Try 6.5 STW. Ballistically they are the same thing, just the wby based round may (emphasis there) have more free bore. I ran the 6.5 stw for a while. Very fast, if you get the twist right it works with heavy bullets. Roughly 150-200 fps fasterbthan the 264 Win Mag, depending on bulletnweight. When I built mine it was hard to find slow enough powders, eventually 7828 showed up, along with the slower RL powders, and that worked better. I got some powder from a company called Thunderbird in the US, basically surplus 20mm cannon powder repackaged. That worked well, but when it was gone, I found out the company was too, and that was that for that. Some of the 50 BMG powders out now would likely work well. Not a round you'll get a lot of barrel life out of though. But for a LR hunting round, hard to beat. Except by the 7mm version, of course. - dan