Just speaking in generalities, the 1:48 twist barrel is a compromise between the faster 1:28 twist barrels designed to shoot sabots, and the 1:60 twist barrels designed to shoot patched round balls.
Also, generally speaking, shallow grooves like .003-.005 are designed for sabots while .008-.012 deep grooves are designed for patched round balls.
As I say, many of the current guns are using a 1:48 twist with a .005-.008 rifling depth. They are a compromise.
This is not to say they are bad. In fact, they will often proove to be much more accurate than the shooter is.
You will see many of us saying the modern In-Line guns will shoot poorly with a round patched ball, and often this turns out to be true. IMO, the culprit is the shallow depth of the grooves, not the rate of twist. Shallow grooves don't seem to be able to get a good grip on the cloth patch so it often slips or skips over the grooves.
IMO, this slipping can cause the cloth to tear and burn thru. If that happens, the high pressure gas leaks past one side of the ball and deflects it as it leaves the muzzle causing erratic groups.
The 1:60 twist barrels usually don't have a fast enough twist to stabilize long bullets so the bullets may turn end over end, or wobble while they are in flight. This wobble will produce unpredictable trajectories and create the "keyholes" often seen in the target or hide they hit.
