Sellier & Bellot 180 gr. SP. with a 2x scout set up. I used it for hunting in several M39's, and it's always consistently performed 1" moa or less if I do my part. After the prices went up on the M39's, I stopped dragging them around the woods and started using a K-31 (wich is actually much handier) and just as accurate.
Check out some cruffler sites like gunboards or Parallax... accurate Finns are the norm. It's about free floated barrels, two stage target grade triggers and good ammunition. If you reload... even better. I know people have been reloading using .308 bullets with excellent results. I'm sure Norma would do the trick, but as we all know it's dam expensive. I've said it before, surplus ammunition won't shoot any better out of an M39 than it will out of a new production RemSavChester. Surplus, is minute of man.
This is my one of my old hunting rigs
When the Sako's got to be worth more than the B-barrels... I put the scope on the B, and relegated it to my back up rifle. I prefer the K31 for a couple reasons.. the safety is easier to manipulate with cold fingers, the ability to mount a traditional scope with a non permanent mod mount and the fact that the offset scope allows the use of iron sights. Very nice to have when the prey comes running past you at virtually point blank range. It's also a little shorter and easier to move around with. The ammo availability is a bummer though.
Also, (if it matters in a SHTF situation)... there's retail value. A new production gun will decrease in value the minute you buy it. The milsurps hold their value, and more often than not.. increase. And, like most weapons built in the '40s, they're built to last.