I only use steel in my Pap, SKS and Makarov pistols. Since they are all Russian based, they seem built for it and have no issues.
I have heard it does cause more wear to chambers, extractors, ejectors. How much? And when it will cause problems? I dont know.
I would never use steel case in an AR, I have seen two different times at the range where people shooting steel case out of an AR got spent cases jammed in their chamber that the range officers had to bang out with a cleaning rod! It wasnt a pleasant sight!
These are the retard professors teaching our kids. He has no right or knowledge of fact that ANYONE will use it offensively. "certain unnamed percentage" yea right. More bullshit from a liberal professor. He has no qualification to make that statement.
Law is sketchy, but technically they can't tamper with evidence, and if its configured as a complete weapon then there are no "parts".
The ATF has similar rules for NFA weapons, and they do not treat complete weapons as a "parts bin".