Looking for assistance interpreting barrel markings on a commercial Mauser Oberndorf for sale.
On the left side of the barrel is the serial number 852XX and 6,5 S.P. On the right side is BS 6,5.6,72.200 M.
The barrel serial number indicates it is from 1922-23.

I understand the barrel to be 6.5mm bore, 6.72mm groove and 1 twist every 200mm.

So my questions are:
What caliber is this barrel - 6.5x57, 6.5x54, 6.5x55, something else?
What is the S.P. stand for - Schwedisch Patrone, Spitz Patrone?

I need to buy a Jon Speed...

Any help is appreciated!