Depends on what you want to Hunt.
I use a couple different bullets for MN Whitetails. The 123gr Speer and Hornady .310 work great, your rifle will most likely shoot one better than the other. Try em both.
The Rem and Win are junk as far as I'm concerned. Never could get either one of them to shoot.
Sierra .311 can be very accurate, but they are too hard for the anemic velocities of the x39.
Barnes makes a .310 hunting bullet, but I have not tried it.
For plinking and maybe even hunting bullets slip on over to GunBroker and look up "bulletguy". He sell seconds at a pretty good priced. I bought 500 Speer 123gr SP for, I think $60.
AA 1680 was designed for the 7.62 x 39, might want to start there for powders.