Most choke tubes that are certified for Hevi-Shot are manufactured from hardened steel. Most chokes that state that they are for "lead only" are made from non-hardened steel.
Some chokes are made from bar stock and some are made from seamless tubing. Since it's not always possible for us as consumers to know what material a manufacturer uses, it's always wise to follow their guidelines.
I hope this helps.
"If he's out of range, it just means that he has another day and so do you."