Everyone is pointing you in the right direction on a powder. You could even try something a little slower too, I know there are some powders available often where I'm at that work well in 300 Win Mag. I've used MagPro for 168gr projectiles and had decent luck. I'd also be looking for some H1000, otherwise go with the slower powders that you have like the Re22 or Re25.
Maybe instead of going down in bullet weight you should've picked up some 180gr Interbond or ELD-Xs or really anything in the same weight, then you'd have a better starting point if you go back to the bullet you wanted to shoot.