Jim B: In addition to my response to your post in one of the other forums I reread your initial post and saw that you had included the 8mm Muaser round in your search for chamber adapters.
You will have much better luck with chamber adapters and the .308 bore. The 8mm is a .323 bore and I haven't found any pistol or revolver cartridges in that bore diameter that would work in an 8mm. I did find, in my older Lyman manual, a number of cast bullets for the 8mm bore, running from 103 gns to 243 gns, but those are for the rifle.
If you want to shoot subsonic type loads through your 8mm, I would suggest the heavy slugs at very low speeds. When I was firelapping some of my rifle bores, the literature provided indicated I should use a very small charge (4-5 gn) of fast buring powder (I chose Unique) held in place by the polyester stuff they make quilts from (fiber bat fill??). I followed the instructions and had a blast using those light loads. The polyester also helps clean the barrel after each shot so if you are using really soft slugs it helps with the cleaning process.
You can get a whole bunch of adapters for pistol cartridges for the .308 bore (308/06/ etc.) but it doesn't look like their is much available for the 8mm unless you make up your own wildcat chambering (I would go the heavy slug/subsonic route myself or fiddle with expanding a 32-20 case or wildcatting with a necked down 38/357 case). HTH and Just a thought. Mikey.