I had 243AI build 2007 on Rem 700 action with 27" long Hart 1/10 twist barrel wanted it for antelope been kind of safe queen. Powder I was interested in using was IMR-4007ssc ran it in a 30-06 was pretty good.
Hodgdon manual had max load of 45gr/IMR-4007ssc,80gr Sierra @ 3319fps. I worked up to that max load used a Rem Core-Lokt HP 80gr @ 3425fps worked up to 47gr @ 3654fps. I shot few 87gr Hornady and Nolser BT 95gr (shot those in a 6RemAI) and I never chronograph any of those loads.
I've never had much luck with R-19 or 22 but have had pretty good luck with R-17 and I need to try that in the 243AI. that rifle is one of my project for this coming year.
Sound like you had had fun putting that rifle together. Well good luck