Kestrel;
I shoot a .338 Winchester magnum & reload for it. It's an older Tikka Whitetail with a 24" barrel on it.
I've found that the Hornady & Speer manuals couldn't be much further apart than when dealing with this caliber's reloading information. I prefer to use these two manuals because they both use real guns to develop their data, not test barrels. The Speer used a Winchester mdl 70 and so did Hornady, both, as noted above, with 24" barrels. Yet the starting load in Speer for RL19 powder exceeds Hornady's MAX load for 225 grain bullets with that powder. Other powders vary widely also, yet some are quite close. I carefully worked up my loads, I can tell you that fer sure, fer sure.
I tested RL22, RL19, N160, and IMR4350. I'm still running chrono tests on the gun & loads, but it's more in the nature of fiddling than work-up.
Current hunting load is 75.5 gr of RL19 in Winchester brass that's neck sized only, with CCI magnum primers under the Hornady 225 gr spire point. I'm getting 2875 muzzle and S/D's in the single digits with very nice accuracy. I'm also getting 8 reloads per brass, so I'm pretty sure this isn't a real high-stress load.
900F