I just looked up CIL 266 on the numrich site. 99 percent certain now it's a Stevens/Savage/Springfield gill gun.
Interesting form of semi rimfire, with a few variations....(ie: not all have gills, or the same number of gills) In some the charging handle can be pressed into receiver to lock the bolt. It then becomes a bolt action. Some will cycle s, l, and lr but only function as a semi with lr. When fired the spent case is ejected, but the bolt stays back until the trigger is released.
The few that have passed through here were quite accurate. The ones that worked worked very well, but I did send one away as parts because I just couldn't get it to purr (lol clackety clack).