My full auto MG42 shoots in .308 just fine without changing the nozzle. Semi autos are on the borderline of having enough recoil to operate the gun, and therefore are more likely to need a booster with a smaller hole. Try it first and see if it works with the nozzle you have. There are so many variables with semi guns that just one solution doesn't exist.
Nozzle sizes are listed in HDv 216/6 for German guns, Yugo kits had a lot more different sizes.
All you can do is try it first like John suggested.
Depends on ammo and how loose or tight your gun is. That said, if if does not run in .308 you can try getting a .308 booster cone like the early MG1's used (which is hard to find now) or get a MG3 flash hider and barrel bearing (they are meant to work together) from RTG which should give you the pressure needed. Mine (in semi) will run well with a 10mm cone with the .308 ammo I have.
Another option is, you can weld up a larger orifice cone and drill it back out to 10mm or 9.5mm which should give plenty of gas to operate your gun.
You want the least amount of gas needed to make your gun run as not to beat it up. This is why I like to have various sizes of booster cones to fine tune depending on ammo in my tuning kit. I have 10mm, 11mm, 11.5mm, 12mm, and 13mm cones, plus the MG3 type.
I start with the largest and work my way down till it runs reliably. Semi's are bit more finicky and need a bit more gas due to added drag, but the same principle applies.
