I've picked up a couple of the UK59-ammo-belts for trial during the R&D period of this......and have three (3) MG42 Bolt-Heads with the bolt-face machined to correct diameter for 7.62x54R rims.
I've also picked up 7.62x54R chamber-reamers for this project.
The next challenge seems to be "head-space" gauges. So far, the "industry" seems to see the 7.62x54R as a cartridge that head-spaces off of the cartridge-rim..........and not by how much room/space there is between the rear of the chambered-cartridge-rim and the bolt-face when the bolt-head is locked onto the barrel-extension.
I will continue to look for a source of full-length-type cartridge-case-type head=space-gauges.
If gauges cannot be found.......for my barrel I will try using SAAMI-Specs. for chambering..........or +.002" frr-space off the head of a know good cartridge-case (??).........or (??).
I'll also see if I can get some information from Bob-Naess reference using "used" 7.62x51mm/.308 barrels (like a well used MG3 barrel-assembly in .308).
I still have to look at:
1: Extractor-modification to retain "rim".
2: Top-Cover and Feed-Tray modifications for feeding.
3: The some other "adjustments" of parts at the first range event (Booster-Cup/"Nozzle", etc..).
US Army, RetiredBlanksguy2001@outlook.com