I have been shooting the 338-378 fronm the time it came out.I have had to research and almost make my own data.When I find data for the 300 gr bullet .I use it to start with for bullets such as your 285 gr bullet.I am fixing to do the same thing myself with the 285 gr barnes bullet for the 338-378.I have only used reloader 25 powder with alot of luck.I have gotten .25 " groups with it and 250 gr Nosler Partitions at 100 yards and just under an inch at 300 yards.I have also target shot 300 gr serria match kings ,275 gr swift a nd 275 gr kodiak bullets.I really like the 338-378 .Be sure to clean your barrel at least every 50 shots or it will shoot like a shotgun.If you have any questions give me a holler.I found a powder that will shoot a 300 gr bullet at 3000 fps or a 275 gr at 3100 fps out of a 26" barrel.I am going to try this powder with the 285 gr barnes.I have a bunch of old H-870 I am trying too.Be careful it can go from no pressurer to alot fast within a grain of powder.I like the Nosler partition 250 gr best on moose and bears and elk.It hits like a mack truck.We will see how this barnes 285 gr does.