You’re talking basically about zip-guns, staple of inner-city violence from a bygone era, and they were outdated once criminals got the wherewithal (through strong-arm robbery or welfare bucks) to illicitly purchase “the real thing”.
The new legislation that will come in the wake of small-business “arms” manufacturing, will take the form of the kinds of laws in place prohibiting illegal marijuana growing and moonshine stills.
This is not small business manufacturing but personal manufacturing. This technology is still in its infancy and many improvements are needed to enable parity with "the real thing", but feasibility has been proven. Any number of laws can be passed to attempt to prevent this of course, but these will be laws against information being exchanged, not goods. The point that by prohibiting the traditional retail distribution of arms is not going to cause arms ownership to shrink to political insignificance.