I don't have an Ultra version, but my Handi-Rifle in .223 has a 1:9 twist barrel and it delivers its best groups with bullets in the 60 to 69 grain range. Mine doesn't shoot 55 grain loads very well in comparison, and it especially dislikes the Remington / UMC 55 grain FMJ stuff that Wal-Mart sells.
I envy those who have Handi-Rifles that DO shoot that Remington / UMC load acceptably well, because it is cheap and plentiful at my local Wal-Mart.
But I'm not complaining, because I wanted good accuracy with 60 to 69 grain bullets anyhow, so I got what I wanted in my Handi-Rifle.
YMMV and all of that, but if yours doesn't shoot 55 grain loads well when you get it, you might find, as I did, that it likes a wee bit heavier bullets.
-JP