I purposefully used the title to draw the eye of those among us who shoot Paper Patched bullets in their BP rifles either for competitive shooting or hunting. I have searched the forum for discussions regarding paper patching and the results were interesting to say the least. A lot of myths regarding the use of PP bullets were promulgated here as well. Having grown my library reading the published literature regarding the use and rolling of PP bullets, especially the tomes of Paul Matthews, and having "rolled my own" and shot them now for 5 years, I have an understanding of the making and use of the PP bullets in my 1885 High Wall as well as the Sharps rifles. I can alter the seating depth of the bullet to make them cycle in an 1886, but they work best in that rifle as a single feed directly into the chamber. Know however that use in the 1886 was an experiment, not a steady diet for that rifle.
There are two ways to go with a PP bullet - either Bore size or Groove size. Groove size necessitates a shorter O.A.L. and therefore a deeper seated bullet with the associated loss of cartridge case volume and powder space (a lower powder volume and less velocity). Groove size products can utilize either black powder or smokeless powder to launch the bullet. Both have their upsides as well as their pitfalls.
Bore size PP bullets REQUIRE the use of black powder and its associated burn characteristics to "bump up" the bullet at shot start and obturate the bore and take the rifling. The bullet actually swells up from the top down as physics take over and the bullet gets shoved up into itself from inertial laws. (The base starts moving into the non-moving tip and expansion occurs)
Smokeless propellant, with its slower pressure buildup, will not expand the pure lead bore-size bullet properly into the available windage, and accuracy will suffer. Bore size bullets made with anything other than pure lead will likewise fail to expand due to their hardness. Only pure lead bullets will suffice for bore sized products. The bullets used for my 45 caliber rifles are .442" in diameter and when wrapped are .449" in their final diameter. They do, in fact, obturate up to groove diameter, if and only if black powder is used to launch them.
I would like to ask anyone on this forum who shoots Bore Sized PP bullets in their BPCR if they have tried a BP substitute like Pyrodex or MP-Black if it works like BP to obturate the bullet. Since these propellants are basically smokeless powders made to stink and leave black fouling all over the place, I don't see how they can emulate the actual burn characteristics of BP which is a Class-A explosive.
I can't seem to find any published information regarding this from any of the works available by respected authors or industry experts. I am sure that theory abounds but actual data would be welcome. I have tried it but my results (at 100 yards) were not definitive. Of course old eyes and open sights probably had more input into the target than the propellant used. 
With rifle in hand, I confidently go forth into the darkness.
