Get yourself some triple 7 3f loose powder and buy some of the new Hornady SST or Barnes MZ-TEZ bullets that come in 250 grain weights. These bullets are very accurate with 90 or 100 grains of powder and have high velocities with the triple 7 powders.
Uncle is shooting 250 gr. TC superglides sabots. 90gr 3 f 777 and Federal Fusion primers. They have produe the best groups for him. The primers made the difference. He tried 3 brands and the Fusions were the most consistant.