David, the only thing I can say is my 500 with essentially the same Barrel/Bore and my 590 have been shot with Steel and Tungsten shot without issue Sir. I'm talking over 8 years for what it is worth to you. It's a shame that Mossberg won't say in my opinion.

David, If your not hunting where you need steel why worry about it. If your using it for home defense lead is fine. When the company (Mossberg) doesn't say no problem why bother? Lot of shotgun option out there that will handle steel shot no problem.