just compare the measurments by yourself

but it looks like the 308 shoulder is much bigger so the chamber reamer dont clean it up. better to start with another barrel blank.
I dont know if anyone making barrels for the .318 now, maybe american custom barrel maker but in australia? lothar walther in germany dont offer them.

if you find a french machine gun barrel for the 8x50R lebel, the 8 mm lebel shoots a 8,30 mm bullet what I think is fine for the 8,32 mm of the .318. machine gun parts are restricted in many countrys but if you cut off the chamber its a common barrel blank. this way I made my 7,62x39 Carcano barrel by using a finnish maxim gun barrel in 7,62x54R were the orignal chamber was cut off before.
machine gun barrels are usually very thick in diameter.