Had one, couldn't get it to perform with ANYTHING. Terrible barrel with problems beyond the twist! Replacement 1:28 barrel is much better.
Run a tight, lubed patch down that bore, go slow, and tell us what you feel. Nice and smooth with even pressure all the length of the rifling - or something else?
Some guys got the 1:20 barrels and had good luck with them, so I think a lot more was involved than simply twist-rate.