The few people that I’ve read about that have built a .308 pistol will tell you they’re just too big.
How about a 7.62X39 on an AR-15 platform? Lots of cheap ammo available and you’re still shooting a .308 bullet. I don’t think there is enough burn time in a pistol barrel to give a 7.62X51 much of an advantage over a 7.62X39 anyway, but if you’re looking for a flame thrower
