My father just had one finished last year as a switch barrel with a 6.5x284 as his other barrel. Not sure what bullet weight you want to use but I did the work up for my father's rifle with Sierra's 120 gr. HPBT GameKing bullet. I did some very limited testing with Nosler's 110 gr. Accubond since it wasn't shooting very well out of a 257 Rob AI. Here is what I have for both bullets:
110 gr. Nosler Accubond
56 gr. N-170, Fed. 210, necked down Lapua 6.5x284 brass
3199 fps 4-shot avg., 0.498" 3-shot group @ 100 yards
52 gr. H-4831SC, Fed. 210, necked down Lapua 6.5x284 brass
3176 fps 4-shot avg., 0.392" 3-shot group @ 100 yards
120 gr. Sierra HPBT GameKing
49 gr. H-4831SC, Fed. 210, necked down Lapua 6.5x284 brass
3001 fps 4-shot avg., 0.352" & 0.453" 3-shot groups @ 100 yards
I had really good luck with H-4831SC in both the 25x284 and 6.5x284 barrels. Let me know if you want any more details regarding these loads. As always, reduce these loads accordingly as your rifle and components will likely be different. Almost forgot to add that the barrel is 26.5" long.
Kevin