They were sighted for 173gn flat base round nosed projectiles, that could be your issue with accuracy depending on the bullet weight from the PPU you are using.
I use S&B (Selliot and Belot) 173 gr. You might try it. At 35 yds I have about 3” of spread, so this ammo works well for mine. My rifling is likely not as good as yours too, from what you said (mine bore is about gone). BTW, nice rifle and well done!
