Dennis,
Pope's patent can be found at Google patents here:
https://patentimages.storage.googleapis.com/47/50/60/ed1a4398e7fe68/US384277.pdf The fit is so good between the taper on the barrel shank and the adapter that fits into the receiver, that if I put the barrel into the receiver without that knurled collar it's very difficult to break the barrel free! I tried it only once and had to tap the chamber end with a brass punch to break the contact free of the two! There is no gap between the barrel and the receiver adapter when it's fully seated.
The procedure to install a barrel is to spin the knurled collar on the barrel, ensuring the end of the collar is behind enough the chamber end of the barrel is revealed. Then insert the barrel into the action and begin tightening the knurled collar onto the action. As it's hand tightened it will seat the barrel shank and the collar will bottom out against the action.
There's a small hole in the collar and a spanner wrench with it. But I've not used the spanner wrench, and I believe it's only there in case the collar is twisted on too tightly by someone, and the spanner would help break it free.
We counted the threads on the barrel, and on the adapter, and I believe they were about 21 tpi and 23 tpi each? We calculated the barrel is moved about .015" in or out depending on whether it's tightened or loosened. Just enough to draw it tight, or break the contact on the taper. There's also an alignment notch in each barrel to maintain vertical commonality between the 3 barrels.
It will perfectly zero each time, not matter which barrel is used, or how many times it's on or off. Just amazing workmanship, and engineering by Pope.