Go to link and go to the part about ‘Constriction’, figure ‘G’ is a jug choke.
https://en.wikipedia.org/wiki/Choke_(firearms)
What it does is let the shot spread out in the ‘jug’ and then be constricted back down to less than bore dia.
It wouldn’t effect a solid bullet at all, but shot would be choked down before it leaves the bore.
It isn’t that hard to do if you have a lathe. It would be a piece of cake to put a ‘full choke’ jug choke in a old 22cal rifle barrel.
12” of regular chamber/rifling, then ream out just the rifling. Then a jug choke of 1 1/2” one 1/2” or so before the bore.
I have thought of doing that.
It would be great if you would try it and report back.
The old guys were not fools. There may be a reason they kept the oversized Routledge bore not constricted.
I think the idea of being able to use the rifled barrel, and have good patterns with 12 inches of smoothbore later, is a great idea.