Yes, but the most important parts, the parts that legally constitute a gun are being printed in plastic. The parts you’re talking about, do not legally constitute a gun. Sure, you can’t make a barrel, bolt, or firing pin out of plastic, that’s obvious, but those parts by themselves are not guns under federal law. The “firearm” is legally defined as the lower receiver or frame (the part that holds the trigger and magazine). If you want your gun to be untraceable, if you want to have a gun but not be a registered gun owner, you just need to manufacture the frame or receiver. Which in the case of small frame AR, just looks like this:

It’s just something that holds all the other “non-gun” parts together into a “gun shape”. The round is never housed inside the receiver to be fired, and thus the plastic is never exposed to the internal forces of firing the round. Pistols experience more force, since the receiver holds the slide rails and are more impacted by recoil, but they still do not house the round, or need to contain the internal force of firing the round.