I shoot a McMillan TAC 338 Lapua and have developed three great shooting repeatable loads. A 300gr Berger over Retumbo at .015 off the lands shooting 2720fps isn't setting speed records but it is very accurate.
The 285gr TSX over Retumbo shooting 2840fps is a great shooter, my best 500 yard group was 1.6", the others are very close but have superior BC's for better long range shooting. I worked up the TSX load for an upcoming Elk hunt.
Another good shooter is the 250gr Lapua Scenar over RL-25 shooting 2905fps. all loads are three shots touching at 100 yards with plenty of speed to get the job done.
The TSX and Scenar are loaded at a length that will feed from the magazine. The Berger is fed one shot at a time. All loads are in Lapua brass and CCI-250's.