Popper sized for what? the historical size of american bullets? or for effective shooting with no fouling?
The american bullets was arguable larger than needed. Resulting in this issue.
In the system used by the British and danish armies the bullet was loaded with the paper and the paper held the grease.
And both had tests showing that is was indeed possible to a hundred of rounds with no cleaning. Because each round pulled the fouling from the shot before it with it when fired.
The british made their bullets smaller a couple of times with no loss of accuracy. They simply underestimated how much the bullet could expand when the first version of the round was designed.
"Colonel Lane-Fox recalls that as First Instructor at Hythe (before 1855), “as many as 150 rounds were frequently fired out of the same barrel” without any fouling or difficulty of loading. Even more remarkably, the rifles were left to sit overnight without any cleaning “in order to make the test severe.” They still loaded and fired “without experiencing the slightest difficulty in loading.”
Busk’s Hand-Book says rifles were fired “200 times successively without any difficulty in loading.” "
Taken from
https://nebula.wsimg.com/a1ee616841...C5D56582B54161E90&disposition=0&alloworigin=1
I highly suggest reading it. It tell both about when the enfield was seen as "perfect" with this cartridge and how it was almost taken out of service because the same cartridges didn't work when transported to other parts of the world. (and show why Minie was a rather minor person in the story of the rifle musket)
And danish testing in the late 1850ties show the same. Firing bullets all day, letting the weapon stay dirty over the night and then firing again the next day. And it note that the last shot was just as easy to load as the first shot.
And in that test the P53 was tested against danish made rifle muskets and against up-rifled muskets.