Proteus at the DefCad forums has published CAD files for “The Brick”, a 3D printable semi-automatic .22 LR pistol. The gun is mostly made out of ABS plastic, even the bolt and barrel, but it does require a number of metal components, including an AR-15 semi-automatic fire control group, firing pin and buffer spring as well as a Ruger 10/22 magazine spring, a 1x8mm metal insert (for the chamber) and .44 caliber lead bullets or equivalent (inserted into the bolt to provide weight).
As far as I know, this design is theoretical and nobody has actually fired it. Given the venerable .22 round’s rimmed design is infamous for causing feeding problems, I am going to remain skeptical that consumer 3D printers are a practical, and safe, method to produce semi-automatic firearms in their entirety.
Many thanks Eric for the tip.