BAW,

The following is from Geogre Nonte's "Guide to Cartridge Conversions."

Make cases from new 45-70 brass, trim to .204" and turn the rim to .560" dia. Full length resize in a 33 WCF die, size the neck down and push the shoulder back in an 8mm die until the case will chamber, then fireform. Use .323 bullets. Sounds like a shitload of fun.

Wallace I think leftoverdj is on the right track. the earlier 8x50 siamese was a .318 bore and the later 8x52 was supposed to be .323. Are you sure you have the 8x52? As with most military barrels ,who knows ? Slugging that barrel would be a good place to start.