I have heard Adams Arms pistons handles steel ammo pretty good. Actually, the only malfunctions I know of with their piston system was on the sons of guns "Desert AR" episodes, and that was mostly due to malfunctioning people putting a gun together. I wouldn't get it just to handle the steel ammo, but if you are going to get an add-on piston, Adams Arms seems to be the way to go. Pretty new to manufacturing the whole AR, but I haven't read or heard anything bad from people who bought them. If they don't cost too much, might be worth a try.
"Democracy is two wolves and one sheep voting on what to have for dinner.
Liberty is the well-armed lamb contesting the vote." - Benjamin Franklin