Hello AH.com members. As you can see I'm new here and have a .416 Rem Mag reloading question using 400gr Barns TSX and Varget powder. I got load data from Barns and am attempting to use 75 grains of Varget with this bullet and seat them to 3.590 as they recommend. After seating these bullets to that length the next day the OAL has increased +- .030 making them function unreliably in the magazine of my M70 SE. I started with new Hornady brass that I had full length resized with new RCBS dies. The neck tension is evidently not great enough with this compressed charge. Is there a powder better suited for this bullet or is there a trick that I don't know of?