I haven't tried RL-12, But I have used WW 748, IMR 4895 and AAC 2520. However IMR 4320 is my favorite, and the powder Jack Lott recomended. I have several old articles by him. I had my Lott made up by the late Dick Nickels of Ridgetop Sporting Goods in Washington state, back in 1992. It was the first one he had ever done in that caliber. If anyone else had a Lott made by him I would like to know, as I supplied him with the chamber reamer. I don't want to give any powder charges as my gun will take substantially heavier charges than normally recommended.