My son and I signed up for the October Gunsite XLR class and did the read on the 338 Bullet test article. We followed the finding and decided to go with the 285 grain Hornady rather than the Berger 300 grainer that I have been stocking up. We have been hording Retumbo and have sufficient jugs to last a couple of barrel changes. We made that decision after reading Frank's (Lowlight) comment. We were able to get the 300 grain Berger to 2850, but we want to keep that for next XLR class with a different 338 chamber.
This is what we did with 24 boxes of Hornady, ogive sorted them and pointed them with Whidden's bullet pointer. We then weight sort them into groups and found them vary wider than the Berger or SMK. We have Marc Soulie of Spartan Precision Rifle chambered 2 barrels with Pacific Tool and Gauge 338 Lapua Magnum Tactical Match reamer. This have a slower entry and more flexible for our loading. The load development sessions were tedious, we started with CIP magazine length, but we settle with single loading length for we want max speed for the class. We start the testing from 92 grain Retumbo with bullet touching land and went up .5 grain till we found the speed we want. The two barrels shot 1/4" to 3/4" groups at 100 yards with just about anything we put through it. I wished I can do more testing with longer distance. We found that the most consistence and lowest SD seating length with 96.0 grain of Retumbo is between 3.049" to 3.051" cartridge base to ogive (0.330" gauge diameter). The heavy varmint profile barrels are 28" Bartlein 5R, 1 in 9.5" twist, and 30" Kreiger, 1 in 9" twist. The load give us 2930 fps for the 28" tube and 2980 fps for the 30" tube. Our original intension was to shoot the 300 grain Berger and have the faster twist for that bullet.
We don't have any experience with the 1 in 12" twist barrel, so I do no know how the 285 Hornady with perform with it.
We shot a box of Remington 250 factory load for comparison, they were Lapua brass with 250 Scenars, and those chron at 3100fps out of the 30" tube.
I hope this helps a bit on you load development. We have shot over 500 rounds for the two rifles for the load development, and after the batch of 500 we sat aside for the class we have only a few boxes left to try for CIP magazine length loading. We probably won't buy any more of the 285's after this for we have other bullets we want to try out. I probably would not resist if there is a big sale though.