RE: 300 Winchester Short Magnum
Get on the accurate arms website and request a free copy of their reloaders manual. Many of the factory loading use MAGPRO. This is produced by Accurate Arms. This powder was specifically designed for the Short Mag family of cartridges. According to my chrony I achieve nearly the same velocity as advertised by the factory. My rifle is bolt action and has a 24" tube. Your velocity will probably be a little lower in the BAR.