It's absolutely shure, the caliber is 8x57IR. By this caliber it gave long time confusion between 8x57IR ( 7,7/8,07mm) and 8x57IRS(7,89/8,20mm)written down by RWS handbook Nuremberg 1940.
I use the caliber 8x57IRS and on the box of ammo is written:
"ATTENTION! Only for barrels with the larger S-caliber bores (Bore.310in.,Groove.323in.)
In this book from 1940 aren't any laborations for 8x57IR.
This gun by Aug. Wolf normally takes caliber 16/65 for shot shells in this era, the length is 60mm when unfired