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30-338 win mag

The 300 WINMAG was developed using the 338 WINMAG and necking it down. You basically have a 300 WINMAG with slightly less case volume, IIRC. I would use slightly less than min starting loads for 300 WINMAG.
 
You need to list the powders you have. Most of the loading data is going to be old with mostly IMR powders being used. Sierra #5 has data, all with IMR powders. The two better powders for the 200 gr. bullets are IMR 4350 and IMR 4831.
 
I don't have a way to take a photo of my Sierra page. Hodgdon does have loading data for the 308 Norma Mag. (same as 30- 338) with the 200 Nosler Partition on their web site. Starting and max loads line up in my Sierra manual for the 200 Gr. Match King using your powders. Start low and work up.