Try 40.0-41.5gr of IMR4350 under a Sierra 100gr ProHunter at 2.650”. I’d bet it shrinks those groups to 1.25” or less. My brother had a Mohawk in .308. Free floating the barrel, and reducing trigger to ~3lbs got him down to 1” 3-shots. Ive shot a bit of PPU .243 bullets. My results were similar to yours. My Rem Mod-7 in 7mm08 shoots about the same as your rifle. It’s a big-game killing fiend!