About the twist rates I don't know: I never had the possibility of mesuring one of them, but in here sure that a lot of people knows this exactly...
If I say all I ear about the paper cartridges for Colt and other I can say that I think most of people and not only military had used them.
The first I ear talking were the tinfoil cartridges, in German tin in fact, because the american tin wasn't of good quality in this time...
It was complicated with those cartridges: piercing with a needle, put in the chambers and shoot. The tin let very small unburned balls in the chambers and the yield was not at its best. So Sam Colt and the Col Hazard have made new paper cartridges and the value of the pulp stocks required to supply the cartridges remains in some archives.
After that the paper was treated with KNO³ and some test were made with treating by acids, skin cartridges (pig or sheep intestines leached with potash), cartridges made with powder and collodion (brevets Bartholow and Jonston & Daw), etc, etc, etc...
Concerning the stopping power, the bullets and the accuracy they certaily did something about this, something like a mix, conical bullets weighing more than the round bullets, good powder charges for the stopping power and, may be the best (the case of the 1861 and Remington for sure) : progressive rifling revolver barrels for speed and certainly a best accuracy...
That's all I believe to known in this subject...