My experience with an 18" twist barrel is that a 40 grain bullet (standard in .22 Long Rifle) is the heaviest that can be stabilized at 100+ yards.
This takes us to a maximum known number of survivors of 7 rifles and 2 carbines.
Is the ejected shell thrown clear of the action? Or does it drop inside. And is the left side of the action plugged up so that empty .22 rimfire cases cannot enter?
I learned about these rifles from one loaned to me by Terry Buffum. With that rifle (a Springfield-made Gallery Practice Rifle, not a Stevens-Pope) the empty cases fell back inside the magazine well. After shooting, I turned the rifle upside down and shook it. All the empty cases fell out.
These Stevens-Pope replacement or conversion barrels are fascinating. Most interesting is that the whole idea of using the unaltered Krag action was developed by Harry Pope. And if you look seriously at the whole story of the conversions use and the politics of their replacement, you arrive at the parallel development of the Winchester 52 and the 1922 Springfield.