I used to hear about Progressive Rifling in old guns from years gone by. I don’t hear about them anymore… Which to me seems odd. With modern precision machining, it should be much easier to produce a good Progressive Rifled barrel.
The advantage of this would be much like a Back Bored barred in a shotgun… Less felt recoil and a higher shot velocity. Who wouldn’t want this in a rifle? I guess the modern Polygonal Rifling pretty much does the same thing, and it’s easier to achieve, but not everyone likes the stuff. I know several guys that have a healthy distrust of any barrel that doesn’t have traditional lands and grooves.
I could especially see an advantage in a progressive barrel in calibers that prefer a long free bore… such as most of the Weatherby calibers. In a traditional rifled barrel, the bullet is slammed into the rifling a torqued around rather suddenly into the twisted rifling. This problem increased as the freebore is increased. This slamming can cause deformity in bullets and inconsistent pressures if the bullet is seated at eve slightly different depths. Progressive Rifling would slowly turn the bullet into an increasingly accelerating twist until the bullet leaves the barrel at the desired twist rate… and balance the pressure curves, thereby helping to increase accuracy. With increased velocity and accuracy… that would allow the full potential of any cartridge fired from it.