They have a proprietary method they're pretty darned tight lipped about. It's said to create a super hard surface inside the bore so I'm betting there's some level of a button or hammer forging or both involved. My personal bet is that they cold hammer forge on a smooth mandrel which is undersize to the stated bore diameter and then run a button through for the rifling arcs. Look up Caudle 3-land rifling and you'll probably get what I'm drifting.
FYI, they're having a serious sale right now. It's 30% and you will need to call. A fully set up barrel from them with that discount is impossible to beat. You'll thank me.
Who is having a 30% off sale? (I've seen several different barrel sellers mentioned)