What’s funny is Eugene Stoner, the designer of the M-16 (grandfather of the M4), later developed the Armalite 180, which incorporated the gas piston design, and a folding stock.Reliable as all heck, but the M-16 was in motion and committed to already, so it was brushed aside. Contracts are all about politics and money.
Someone (Bushmaster, I think) has recently reintroduced the AR-180 with a plastic lower. I’ve never known anyone who owns one.