It started out as 28 in Kreiger barrel as a regular 20-250. I just recently had it Ackley improved and they cut about an inch off. I'm getting right at 3850 fps consistently with 40gr of superformance. It is a 9 twist.
You should try a 20-250 AI with a fast twist. Grafs still has over 1800 boxes of the 55gr. Berger in 20 cal. That long 20 cal bullet flies very flat for a long ways. I happen to have a reamer and head space gages too!