The old way, by cutting the rifling grooves into the barrel:
One of the new ways, by cold hammer forging the grooves in:
Frankly they are both frightening as hell! The 2nd video isn’t specifically firearm related, but the process is similar. I cringed every time that hammer came down and struck the object… that’s TONS of force per square inch.
To use a Workaholics reference… both processes are so tight butthole.
Hat tip: Simon, Eric