I have a Harrington and Richardson Handi-Rifle in .223 Remington that has a 1:9 twist barrel. It definitely prefers 60 grain to 69 grain bullets, shooting sub MOA with 60 gr Partitions, 62 gr. FMJ, and 69 gr Sierra MatchKing HP's. I suppose it depends on the individual rifle, but mine doesn't shoot 55 grain bullets nearly as well as the aforementioned.
-JP