I don't have time to put in 100's of loads for 100 rifles. But here is what you can expect from the various 338's. These are confirmed top velocity loads through a few thousand rounds through over 100 rifles. 338 winny and 338 lapua are 26" barrel, all others 28" barrels. Correction, one 338-378 wby was a 30" barrel and all 338-78 imp's and 338-416 imp's were 30"
200 grain, 250 grain, 300 grain
338 win mag 3020-3150, 2700-2820, 2450-2575
340 wby 3175-3285, 2975-3065, 2680-2760
338 rum,
338-300 rum, 3300-3425, 3060-3170, 2750-2900
338 lapua
338 lapua imp 3500- 3585, 3200-3280 2925-3035
338-378 wby 3550-3685, 3235-3325, 3025-3100
338-378 imp,
338-416imp 3600-3725, 3300-3425, 3075-3200
That is the range you are going to hit in unless you have a very slow or very fast barrel. I grouped the 338 rum, 338-300 rum and 338 lapua together because all the data is together in the same range. Same with the 338-378 wby imp and the 338-416 rigby imp. Again, these are top velocity loads. You may or may not see best accuracy at top velocity in your rifle.