Any reasonably good machinist, working with templates and design specs, could construct a fairly good facsimile of a simple pistol, capable of firing a projectile lethal at fairly short range, and with practice, gain enough skills to build some pretty precision and accurate sidearms.
But even crude weapons may be fashioned from common materials and with only a fair degree of being handy with metalworking and joining of parts. May not have a very long lifetime, but these “Saturday Night specials” could find their way into hands of “self-defense”.
https://www.americanrifleman.org/articles/2012/7/24/the-liberator-pistol/
The genie is kind of out of the bottle on containing small arms altogether.
I have always liked the bang stick Tom Clancy made in “No Remorse”. Could be put in a cane or umbrella with little or no problem.