I had a 338-06 Ackley Improved, to tell the honest truth, with 225grn bullets, there was absolutely no difference in velocity over the 338-06.
I had another bbl chambered in something called the 338 Jordan. It had a body with a one degree taper and a shoulder blown out to one caliber neck length. Very accurate but it recoiled as bad as the 338 Win Mag and delivered almost identical velocities with 225grn bullets.
I found the Improved and the Jordan unacceptable, the improved because it really wasn't an improvement and was very fussy, the Jordan because it recoiled as hard as the Win Mag, which was what I was trying to get away from in the first place. bearhunter