While news on the 3D-printed gun front has been sparse as of late, that's less a matter of stalled development than of the new technology already becoming old hat in this fast-moving world of ours. How else to explain the lack of coverage even as repeating pistols are knocked out on desktop equipment? Consider, for example, the Hexen pepperbox, which has stainless steel liners for its six barrels and is undergoing constant strengthening and improvement as discussed over in the DefCad forum. The video below shows the Hexen successfully fired (actually, it appears to be a related five-shot model), using 6mm Flobert (low-powered .22) ammunition.
The designer, Franco, even printed ammunition holders for the pepperbox, along with a tool for ejecting expended cases (both pictured above).
The video below shows an animated breakdown of the Hexen. You can see the inner workings of the gun, as well as the steel liners for the barrels.
In just a few short months, 3D printing of firearms has gone from a lower receiver, to a single-shot pistol to a rifle to a pepperbox repeater. All of this development has been pursued and achieved by activists and enthusiasts without institutional backing.
Let the wailing and gnashing of teeth by control freaks left in the dust commence.