This is really good, a completely homemade all steel .25 ACP, the "Krikit 25." Even the barrel is homemade, and it is
not a smoothbore. This apparently first appeared on the Interwebs four years ago but I'm only just discovering it. Mostly it's just basic metal-working skills and spot welding.
Video of the process is
here.
Decent resolution photos
here.
Templates and parts list is
here.
I'm not sure if it's the same guy but I see teasers about a DIY .380 called the Kolt.