Larcher,

The 9x57 was a standard caliber developed by Mauser and used in their commercial rifles. It is identical to the 8x57 except for the larger neck and bullet.

The 9x57R is the rimmed version for use in doubles and combination guns.

Both rounds have been obsolete since the end of WWII.

Normal bullet diameter is .355, which is why I feel fortunate that mine is .358 and thus takes standard .35 caliber bullets produced in the USA.

Regards,
Curl