OK, I don't have Sharpe's work but George C. Nonte in The Home Guide to Cartridge Conversions, 2nd 1967 edition, says" use .30-06 case. "Full length size in 8x56 M/S die. If die not available run into 8x57mm die 0.040" deeper than usual or until bolt will close... Use plenty of lube on head and run case into die 2 or 3 times to ensure that head is swaged down to .460" and will not spring back".

Max case length is 2.205", so trim 10 thou off that.

I'm guessing from this info that Walter, who had the converted British rifle, might have had .040" taken off his 8x57mm FL die. Converting the shellholder would be better (as you could still use the factory die on 8x57 Mauser cases), but if you do this be very sure to permanently mark the modified shell holder so you never mix it up with a regular shell holder or you'll have big head-space issues.

Ken Waters wrote about his 8x56 M/S in Handloader 175, (June-July 1995), which you could get as a back-issue off Wolfe Publishing. He used a Lyman X-2 shell holder because it had a lower profile and this meant he could size his US made 8x57 Mauser cases closer to the extractor groove, again to make sure the head was sufficiently swaged by his Redding 8x56 M/S dies. He had an original Mannlicher case that measured .460 compared to .467" on his Remington 8x57 Mauser cases. Without this swaging, they would not chamber in his rifle.

I use Norma 8x57 Mauser cases in my 8x56 M/S and use RCBS dies and .323" Teilmantel RWS bullets designed to open properly for velocities around 2,100 fps. The bore slugged at .323 and I haven't heard of .318" ones, but that's not to say you shouldn't slug your bore to be sure.

The shoulder in the 8 x 56 M/S cartridge drawing is shown as .424" and the shoulder as 22 degrees. The 8 x 57 Mauser is .431" and the shoulder 20.48 degrees. This suggests to me that, the right set of 8x56 M/S dies will work the brass less and your cases will last longer. So perhaps spring for the CH4D dies. I have a set in 9x56 and they do the job nicely.