Maybe the tags were not "politically correct" ?? Classified data ??? Proprietary info ???
I wonder if these were in the Enfield Pattern Room collection ??? The Brits have become super squirrels about gunstuff to the point of lunacy in recent times.
Looking at my steel catalog, the closest fit I could find for a CETME-based receiver was 1-1/2" Schedule 80 steel pipe. That's 1.90 OD, .200 wall, 1.50 ID - just bore the end a bit to accomodate the trunnion, and turn the OD to whatever strikes your fancy.
From what I've gathered browsing the H&K fora, the G3 and CETME use plain soft steel for the receivers, about .060-.063 thick. So you could turn the pipe OD down on the lathe to 1-5/8, or whatever you felt happy with.
I was at the steelyard today getting some other metal, and asked about the pipe. Not everything in those catalogs actually exists; or more properly, it's a "standard size" only if you'll commit to buy a railcar-load after they set up to make it. It turns out 1-1/2 Sch 80 is a very common size, and they had a bunch in stock.
I notice that AC Spruce Co lists 1 5/8 inch OD 4130 CMS tubing wth .058 inch wall and 1.509 inch ID in their catalog. It costs more than pipe though but it might save a lot of remachining and povide a stiffer tube.
That Sterling on steroids would look very nice in 5.56mm as an SBR. The German VG-1 gas delayed action could be adapted to the Sterling style. A fluted barrel such as the HK 5.56 uses would be needed with that type action.
You didn't know about Iron Sky? Then you probably haven't come across Star Wreck: In the Pirkinning. The movie is in Finnish, but there are subtitles in English.
Star Wreck: In the Pirkining : Free Download & Streaming : Internet Archive
What happens when a bunch of crazed Finns make a science fiction fan movie? When they're prepared to spend years making it, and to shell out for detailed sets, costumes, and state of the art CGI? You get a Finnish-Russian empire created by some accidental time travelers, which conquers the Earth and goes into space a-viking? And after that, it starts getting a bit strange...
Maybe it's something they put into the alcohol in Finland. Energia is to video as the Leningrad Cowboys are to music - so totally WTF?! whacked out they might as well be from an alternate universe. Except the Pirkinning was just a movie, and the Cowboys are real.
YouTube - Leningrad Cowboys & Red Army Choir - SWEET HOME ALABAMA
"It's reality, Captain, but not as we know it."