Many years ago I went to visit a company in NW Texas that made gun barrels. Not rifle barrels, gun barrels. For artillary pieces, large navel vessels, tanks, etc. They made their own steel: 4330 Vanadium modified, vacuum degassed, electroslag refined. Each barrel forged, heat treated and machined in that plant. You never think that guns that big will shoot through the rifling in so few rounds. Every time the army ordered a tank, they had to order hundreds of gun barrels to serve the expected life of the tank. Your tax dollars at work.