Winchester rifles and shotguns have been made at various locations around the world using various processes.

In the past -- for the first 75-80 years of Model 70 production -- most Model 70 barrels were cold hammer-forged from a solid billet of steel. The exception was stainless steel barrels, which were rifled most likely with the button process.  

The barrels of current Model 70s are likely button swaged. A process that offers a similar outcome in terms of accuracy and strength to hammer forging. 

You can generally acheive1 MOA accuracy of three-shot groups from a current Model 70 using a properly managed barrel, quality match ammo and superior optics under ideal weather and range conditions.