I haven't loaded Magpro in the 6.5-284 but I have loaded it in the similar capacity 270 Winchester and the slightly larger 280AI.
It is a superb powder with accurate metering, great accuracy, and outstanding velocity.
When I couldn't find 280AI Magpro data I sent an email to Accurate and I got all the data I asked for directly from their Head Ballistician.
You may wish to do the same.
http://www.accuratepowder.com/contact-us/
If you don't find the data you're looking for then I would begin loading it at the starting loads for the 270 and keep an eye out for pressure and an eye on your chronograph.
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