If you make a habit of blasting 4 or 5 magazines at the end of your shooting sessions you need a “machine gun steel” barrel which means chrome lined. The guys who do sustained rapid fire that I know, don’t make a complete 3 gun season on a barrel with 4140, 4150 or 416 stainless. My chrome lined 1:9 barrel is still good after years of hard use. Remember that chrome is for erosion and heat resistance. It still needs cleaning but will clean up quickly with a bore snake.