The minor diameter of a 1/2-28 thread is 0.456", which with a .308" bore means your barrel is going to have 0.074" walls, and a stress riser from the threads. Most barrel makers recommend a 0.125" wall thickness for barrels.
There's a good reason the 5/8-24 thread is used with the 30 caliber, as well as a reason 1/2-28 is not used.
