7.62 X 57

[Jack]

OK, if it's an 8x57 necked down, you can find loading data for the 8x57 using 150 grain bullets. Also data for 170/175 grain bullets, for which I'd substitute a 165 grain 30 caliber.
A lot of 8x57 data is pretty mild, but some data is available with pressures matching the 30-06. One good source of full power data is Accurate Arms.
Accurate Arms 2520 is a ball powder that gives excellent results in 308 and 30-06 with 150's and 165's, so I'd start with that if it were my rifle. 2520 is somewhere in the burning rate range of 4895, 4064, Reloder 15, and Varget (roughly), so that should give you a starting point as to powder selection.
I would start by cutting 8x57 data about 5%, and working up.
(BTW, I'm no metric system genius- the cheap Korean surplus ball ammo I buy to run thru my M-1 Garand is marked 7.62x63)