It depends…. lol
If you are going down to a 20” barrel, I would recommend 1:7 if you want to shoot 77+ projectiles.
If you’re gunna shoot 50’s, you can do a 1:12 at 24”
You can lengthen the twist if you’re pushing the bullets faster. Tighten up the twist if you’re going with a shorter tube… there’s a lot of variables to consider.
I went 26” 1:8 for my 223AI. It’s not designed to be carried around in a hunting scenario… It shoots Berger 80’s quite well. I prefer 69 & 77 SMKs, mostly due to availability and current inventory. It has no trouble hitting a 1/3 IPSC plate at 1000y with the 69 or 77 SMKs…. When I don’t miscalculate the wind…. I have not tried 90’s in it, I expect a 7 twist would be required to stabilize 90’s in a 26” barrel.
For a 20-22” hunting rifle, I would go 1:9 and plan to shoot 69’s or lighter.
My $.02