I think this stuff is brand new to the market... the "MP" stands for "Magnum Pistol" and Alliant's online data source shows data for it in 22 Hornet, .357 Magnum, .44 Rem Magnum, .454 Casull, .460 S&W Mag, .480 Ruger, and .500 S&W Mag.
Judging by the charge weight and the "appropriate" caliber...