OK so why then need a faster twist in the pistol. The lighter charge will not strip the patch but the rifling will still impart the 1:70 twist rate. Velocity will be less but the twist rate will still be 1:70 even after the ball leaves the muzzle.
And if stripping the patch is an issue with heavier charges (rifle charges) shouldn't patches fired from a rifle show signs of tearing/shredding from the rifling?
There may be another answer but I can't see it clearly. Does the slower velocity require a faster twist to stabilize the ball? If so, why?

Nobody mentioned stripping. A 1-70 twist barrel twist the ball one time in 70" of barrel. A 1-20 twist only needs 20" of barrel for one turn. Most pistols are only half of that. Let's say 10" of barrel. It only spins the ball 1/2 turn with a 1/20 twist. A 35" barrel will spin the ball 1/2 turn with a 1-70 twist.

So, they're both spinning the ball the same amount. The ball needs to spin to be stable. A 1/70 twist in a 10" barrel would not spin the ball enough to be stable.

Semi mentioned stripping.
I hope you're not trying to tell me that a 1:20 twist out of a 10" barrel and a 1:70 twist from a 35" barrel are spinning at the same rate! If so that is not true. When the projectile is engaged in the rifling regardless of the twist rate that ball will continue that twist rate even after it leaves the barrel.
A 1:70 twist will rotate the ball at a rate of one full turn every 70" regardless of the barrel length (10" or 32").
Could it possibly be the large difference in velocity that requires the faster twist for the pistol?

yeah i guess they (1-60) or (1-70) are hard to get shooting good without a lot of powder and goofing with them quite a bit other wise i had a grrw 1-60 barrel to cut down for the pistol build but the builder said not to take the chance !

Then it clearly has to be a matter of velocity due to the vast difference in powder charges with all else being equal. If this is not the case then there would be no need for a slow twist barrel in a rifle shooting a PRB.
But then again, would it really make that much of a difference considering the range at which you could accurately shoot a pistol? (talking the average shooter here)
I have a Lyman .54 caplock pistol that I shoot 30 gr of FFFg under a PRB and it is plenty accurate out to 50 yards. I would really like to try shooting a deer with it but at no more than 35 yards and have my rifle with me for a back up for a finishing shot if necessary.

velocity could be one factor but there are smooth bore pistols that shoot just fine and iv'e heard of guy's cutting down barrels and they are tack drivers ?? i would probably bump up the powder charge on the .54 pistol if it can take it. put it in the boiler room and should be no problem !

I plan on that MS. That 30 gr charge is wimpy. Going to try upping it in 5 gr increments and see if I can get her up to 50 grs.
The problem will come into play with recoil because of the rounded grip design and having to hold your wrist at an odd angle.

I explained it to you, but I assumed you were intelligent enough to understand what I was saying. My bad.

btw Nobody seems confused but you. Think it might be you?

Muley read this very slowly so you can comprehend. Regardless of twist rate a projectile will continue that rotation after it leaves the barrel. The barrel length has nothing to do with it. If that same 10" barrel had a 1:70 twist rate and you loaded it with say an 80 grain charge it would stabilize the ball the same as if it was fired out of a rifle. Lets make this so even you can understand. If you have two twist rates - a 1:60 and a 1:20 the projectile from the 1:20 will be rotating 3 times faster than the 1:60. At 10' from the muzzle the projectile from the 1:60 will have made 2 revolutions while the one from the 1:20 will have made 6. All the twist does is start the process. It doesn't matter if the barrel is 4" or 40".
Like I have surmised or assume. The faster twist in a pistol may only be necessary due to the lower velocity because of the lighter charge in order to stabilize the ball. That is the only logical explaination. Otherwise one could use a 1:20 twist in a rifle with an 80 grain or more charge and a PRB with good accuracy. But we all know that is not the case.

The problem with pistols, in my opinion anyway, is "skipping" when people overcharge. It happens all the time with rifles but GENERALLY the projectile only skips a couple of inches up the barrel before full engagement. In the barrel of a pistol length, if you charge too much you get skip and very little rifling engagement before the bullet gets out of the barrel.