Well, ole clownone

Number of grooves and depth of those affects pressure. Just that simple. Hense microgroove and its shallowness. The burden of how much pressure lies with the gun mfg. If you added more grooves to a 308 caliber barrel, you better make them more shallow than .3" bore. You have to keep .308" groove diameter. You can get custom rifling from most barrel mfg.