He is using ITX not steel

ITX Shot

ITX shot technology utilizes a proprietary binding material to blend powdered tungsten & iron pellets.

ITX Original-10: Manufactured to a target density of 10.0 grams/cc. ITX Original-10 is hard enough to maintain superior patterning and penetration, yet softer than any barrel steel. Original-10 is ideal for any shooter concerned with shooting non-toxic through their barrels, including double-gun shooters and small-bore shooters.

Only at BPI: We are your exclusive source of ITX Shot, made by TomBob Outdoors. All ITX products are proudly made in the USA.

USAF RET 1971-95 [Linked Image from jpgbox.com]