Re: @ yank lurker ... Gun show
Chances are that if one can afford a 3D metal printer at the present time they also have access to getting it properly heat treated. IIRC, the 1911 Ian mentioned was printed in stainless steel although I don't recall the specific alloy. Yes, there have been mostly all plastic guns made and exploded as you might expect but every one that I've seen the gun was clamped not held in the hand for test firing.
There were a few guys on youtube some time back making slam-fire shotguns from about $20 worth of pipe and other bits from the local hardware store. I seem to recall one went so far as to make a multi-barrel slam-fire seemingly to prove he could.