Designing the 2-diameter paper patch bullet.

[Distant Thunder]

It could be possible with modern barrels and pretty good QC on the bore diameters, unlike the originals, to design a 2-D PPB that would fit more than one rifle quite well. If the seating depths can be worked out to fall in a range of say .080" to .150" it could work. If diameters are too different you might have to use two different papers, but that is doable.

If you end up seating closer to .150" in one rifle the brass length becomes more critical to avoid paper rings, but that too can be controlled.

I really don't know just how much wiggle room you have for good accuracy. I just know, for me, a good snug fit in the bore and a shallower seating depth gave me the best accuracy. Other are able to shoot looser and deeper with good results. With some careful thought and tinkering I'm sure one bullet could do very well in two or more rifles of the same caliber if they have at least similar chambers in the area the bullet rests before firing.

The cartridge behind it shouldn't matter much, other than maybe the wads required. More powder seems to like a wad stack, with less powder a single wad has worked for me. Even with 100 to 105 grains of 1 1/2 Swiss in my .45-90 one wad was all I used. It has to be a HDPE wad in the rifle, but it works.

My .44-100 was the only rifle I ever had to use a "wad stack" in to get good accuracy. I don't know much about multiple wad loading other than to say, sometimes you just have to.