I've heard about 2400 and magnum primers. I have one load with a 158 grain XTP I worked up before I started casting. I followed the recipe in Lyman 49 (including a magnum primer) and got almost the exact same results (also shooting a 4" barrel). Twice around the wheel and my extreme spread was 38 feet per second (13 standard deviation). Seemed pretty darned consistent to me. Cases fell right out.