What works in my rifle: Lapua brass, Lapua 139 gr Scenar, H4350 at 48.7 gr with the lot number I have, CCI primers. I have a custom chamber with a fair amount of freebore and seat the bullets quite long seated into the lands. H4831 and RL-22 (with a Winchester primer) have worked well too. Go to
https://www.accurateshooter.com/cartridge-guides/65x284/ for a comprehensive article on the 6.5 X 284
I haven't really varied my load for 15 years or so except minor adjustments for different lot numbers of powder. Everyone wants to chase the latest magic powder or bullet but on a calm day my setup shoots well under a minute at 1,000 on a consistent basis every barrel so far. Shooting 20 round strings a barrel is lucky to reach 1,200 rounds maintaining match accuracy.
H4350 has a faster burn rate than H4831 or RL-22 and is a little bit hotter burning but it has given me better ES/SD numbers which matters at long range elevation wise.
Oh yeah, if that is a short action you won't be able to use a COL as long as mine and still magazine load. If you do you'll have to single load and pull the bolt to remove a chambered round. One reason I went with a long action.
Work on your loading technique to be as consistent as possible each round. As a final bit of advice, once you have a load stick with it, easy to use up a barrel chasing a load with the latest internet magic powder or bullet.