I've built a couple.
Three actually.
One was built on a non restricted M1 Carbine and it has a 1-15 twist rate with a .308 diameter bore. It's very accurate and very similar to the 30 M1 Carbine round.
Two was built on a 1907, 351 Winchester semi auto. The rifle was a beater but cleaned up well. I sleeved the barrel, again with a 1-15 twist rate and a .308 bore. The magazine fed flawlessly. accurate.
The third was built on a Zastava Mini Mauser that started like as a 223 Remington and had a burst barrel at the muzzle. The previous owner was going to shoot a fish and stuck the muzzle below the surface of the water. It was cheap sooooooooo. It worked well but of course it needed to be fitted to accept a Tokarev magazine. It had a 1-20 twist rate and it also shot well. Labor of love, I wouldn't do it again.
OP, hope this helps.
Don't be afraid to use a .308 bored barrel. You're never going to develop enough pressure to worry about it.
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