Alliant 2400 data for a 250gr GDHP is maxed at 26gr for a 454 Casull. As another person mentioned, it's 31grs for the same bullet in a S&W 460.

It may be a little dirty with 26gr but it would be a good start charge. The 240gr XTP Magnum bullet shank may be different than than 250gr GDHP. I do know the 250gr GDHP seats deeper than a 250gr XTP with the .45 Colt.

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