What was your powder charge? More than 80gr and that may be the problem.

Precision Rifle's bullets are swaged -- as consistent as pure lead bullets can get -- and most guns lose accuracy with them between 80-100gr powder as the velocity gets too high for the soft lead. I've never had lead bullets group well out of any gun with over 100gr powder. I would think cast bullets would lose accuracy even quicker as they start off less consistent.