What the heck is the solution to this dilema?

As a generalization, the rifle doesn't like to shoot as fast as a standard .243 Win. It will handle the pressure, just won't group.

Change bullets and maybe powders.

I've tried many combinations and think a new barrel would be a quicker fix! Have yet another combination ready for next week.

What is the rate of twist of the barrel, and what powders/bullets are you using?

Also, headspace could definitely be an issue. Have you checked out this possibility? Was the chamber a .243 WCF to begin with, and if so, did the 'smith set the barrel back so that it is properly chambered for the AI version?

I saw a guy than incorrectly bedded his 1903 Turkish Mauser, and it shot slower loads more accurately.

Bobby, the rifle is a factory Cooper with a 1 in 10 twist that has always been 243 AI. I've tried 55, 62, 68, 70, 75, 80, 85, 88, 90 and 95 grain bullets! For powder's i've tried VV 540, 550, H4895 & 4831SC, IMR 4895, 4064, 4350, 4831, 7828, and Win 760. Mainly using Lapua brass and some R-P and Win.

This is the best single group the rifle ever fired, what I seek is consistency. The IMR 7828 and 90 Bergers are currently doing well, slowly

I'm sure you've already tried this but have you varied your seating depth at all? You might want to try to seat your bullets .100 short of the where the bullet just starts touching the lands for your faster loads.

Regards,
Chuck

Chuck, Thanks I'll try that once I get a load which shoots consistently well. Actuall have one with the 90 Berger which is quite promising, just need to chronograph it...