Mine's a Zastava (got rid of the ugly stock) that shoots those 139gn SST's very well. I just sold a 308 I didn't need, and that left a pound of Varget being unemployed. I may give it a run in my 22/250.
My Zastava shoots very accurately with 175-grain Speer Grand Slams and the old Hornady Round Nose Interlocks. What stock did you drop yours in?
Off topic a smidge Rev, but do you know what the twist is on the Winchester M70 Fwt is?