I have been using Retumbo for years. It has proven to be decent for accuracy, and very good for stability and lot to lot variations. Recently, with a load for the 338 AX (Lapua Improved), I have had a great deal of variation (by Retumbo standards). Velocity was consistently in the 2975 fps range in cold weather (up to about 40), but since then, with warmer weather, has been consistently about 2900-2915 avg (in temps in the 60's and low 70's). Same lot of primers, same lot of powder, same lot of cases. I have tried to make sure I have proper light conditions for my chronograph (CED MII). Trajectory indicates that it is probably reading correctly, even though I have not had the chance to shoot 1000 yards very much due to wind and rain. So, I have not totally ruled out my chronograph, but think it is probably accurate. In fact, this is the best chrono I have had for not being affected by sun angles and such, as long as I shade it from direct sun at extreme angles early and late. An inverse temperature to velocity is not impossible, Li'l Gun has that problem well documented. But, has anyone experienced velocity going down as temperature goes up with Retumbo?