give dan wynne at mcgowen a call or email, he will set you up with a barrel for the 7.62x39. They use a .310 groove. Bought one from him a year or so ago and built a rifle on an older 223 long action. You will need to send the bolt to SSS to have the PPC bolt head/extractor conversion done also. sold mine to jonbearman here on this site afterwards and he was getting awesome groups with it (under 1/2 inch with factory lapua and under .3 @ 200 with his handloads). Mine was an 18" 1/10 twist stainless varmint contour on an older 110 action with an early stockade stock. Grafs used to carry the factory Lapua 7.62x39 ammo in boxes of 30 for around $30. I think it is the best 7.62x39 factory ammo out there, and if you reload, the best brass after you shoot it.

good luck