I don't know this to be a fact as I'm not a gunsmith but I've been told a bad muzzle crown will have more negative affect on boat tail bullets then flat back bullets. If the person who built it for you screwed up other things, he easily could have done a poor job on the crown as well. I have no idea of your exact situation but it's possible, depending on the shank of your barrel, that a good smith could cut some off the end of your barrel and rechamber it. That will depend on your barrel.
If you're wanting to stay with a 243AI I would contact Travis Redell with RBros rifles. www.rbrosrifles.com
Travis not only builds some very nice rifles he is a very big fan of the 243AI. The 243AI and 6.5-06AI are two of his specialties.
Best of luck to you and I hope you get things straightened out.