We have stated repeatedly our advice NOT to use steel. polymer,bimetalic, and aluminum cased ammo. It is our ADVICE...nothing more or less. We're telling you that using same may/will cause you/your rifle problems. It doesn't void the warranty simply by using it.
That said, our warranty is for the failure due to factory labor or materials. For an ammo caused failure, we proceed on a case by case basis. We do everything we can to try to help our customers. But when/if we find blatant abuse or misuse, or a clear ammo (versus rifle) failure, we'll call it such. Lacquer build up to the point a round won't chamber? Not warranty. Lacquer vaporized when fired and then solidified in the gas tube and carrier key, and gas rings? Steel case seperated or galled? Extractor damaged? Aluminum case torn apart (maybe just the rim, maybe seperated case)? Polymer case where the back (brass) portion has torn off but the plastic is still in the chamber? How do any of those fall under the rifle's warranty?
The first time I had a call from a department about using the zinc-plated steel cased ammo was about two weeks ago, and I gave the same admonishment as I would to anyone else. I hadn't even heard of it previously, and when I called around to various agencies and local departments, most of the training/range officers hadn't either, and those who had heard of it had opted not to use it and were still using brass cased range ammo.