Regarding what Denny was saying about pressure curve, a good example is the 22 rimfire rifle. They tell us peak velocity, with long rifle ammunition, is reached in an 18 inch barrel.
With revolvers the distance between the cylinder and the forcing cone has more to do with velcity than does the barrel length, within reason, like between 4 and 5, or even 4 and 6.
A revolver loses a lot of power through that gap in front of the cylinder. I thought my 22 revolver with 6 inch barrel had a tight gap, but it would not shoot a long rifle edgewise through a spruce 2x4, and a fellow's 5 inch auto loading would, with the same ammo.