Removing metal around a properly stress relieved cut rifled barrel will not promote growth in the bore. I call BS on that. I have braked a few 300 Weatherbys with #1 contour barrels with 1/2"-28 and they were accurate and durable. They were just louder than I can stand so none of mine have brakes any more. There isn't near the pressure at the muzzle as there is at the breech. I think some are over thinking this. I do suggest that you use the largest practical diameter for any given barrel.
I have no idea how a can would fare on a 1/2-28 30 caliber. I don't think it would matter that much what the thread size was as long as it was fitted right.
