What you have, more than likely, is a J.C. Higgins Model 20 pump shotgun. (not unless it is a bolt gun, but I've not seen that choke system on a bolt action shotgun from that era yet.)
I have a Model 20 and it has a similar type of choke that Mossberg put on some of their shotguns some time ago.
That choke simply is turned at the end of the barrel to adjust the restriction.
Some of the earlier chokes had tubes that were changed out and came in a set.
The J.C. Higgins model 20 was made up till, I believe, 1962 by High Standard and were well made shotguns .
Later High Standard continued production in the form of the High Standard Flight King after Sears dropped the J.C. Higgins brand and switched over to the Ted Williams brand.
High Standard also had a Field King model as well as a semiautomatic, the Supermatic, which I believe was called the J.C. Higgins model 60 when Sears sold them in that line.
These were well made guns and were very popular in my home state of New York in the Hudson Valley upstate area and probably other areas as well.
I often saw them in the gun racks next to the Ithacas' and the Ithaca Deerslayer was the ticket back in those days. If one could not spring enough change for the Ithaca, the High Standard was the next best thing and I never heard of any complaints about the High Standard brand.
My gun is smooth as butter and it shoots well. What's real nice is that it is mostly milled and machined with just a few stampings.
The gun I have was used but still looked good and I detail stripped and cleaned it with all parts looking like new.
You got a good one and I hope you enjoy the gun.
