Here's what I know or don't know. I have two Lee's that are marked 8MM. One is a BSA Co and is marked Parker Hale. The second is a LSA Co and is an Alex Henry & Co Edinburgh . Both are marked on the barrels 8MM and British proofed. When I purchased the Alex Henry I also go with it a box of Kynoch 8MM Mannlicher (8X50R) ammunition and some reloads formed from Russian 7.62X54 that were marked 8X50R Austrian. The seller claimed these were for the rifle??? Catalogs I have seen from the 1920's-30's list rifles in 8MM described as 315bore especially for use in India or places the 303 was prohibited in as much as it was a military cartidge. The balistics in the catalogs are identical to those of the 8X50R. I will try to get a chamber case done in the near future and report back.