H Mate
The sierra super roo projectiles are accurate in my sako 223, 1 in 12 twist.
I use ADI: AR8208 powder, I also use the 55gr V-Max, they are my main go to projectile.
I have also used the sierra 55gr Blitz king, they are accurate as well.
You will find that you will get many varied responses to this question you asked. Different people find different results with different powders.
You will have to find what works in your set up.
I went with the 55gr Hornady V-Max, because I have been able to get bulk projectiles from Clever firearms in QLD cheap.
If you aren't going to do that much shooting, you may find it cheaper and more convenient to buy bulk Outback 223 ammo.
The pre-loaded 55gr Blitz king are a good varmint cartridge, and quite accurate.
Good luck