LongShot space are a SF Bay Area company who have resurrected the hypersonic projectile launcher with an eye to scaling it up to the point it could launch payloads into space at a lower cost that traditional rockets. And while this lofty goal is a long way off, they do have a contract to build a launcher able to throw test payloads at mach 5 for the Department of Defense who want to test hypersonic payloads.

This is by no means a new idea, in fact I made a video about gun based launchers over a decade ago    • Real World Kerbal Space Program - Gun...  
However a more scientific discussion is found in this paper:
"A comparison of distributed injection hypervelocity accelerators" A. J. Higgins
https://www.researchgate.net/publicat...

Follow me on Twitter for more updates:
  / djsnm  

I have a discord server where I regularly turn up:
  / discord  

If you really like what I do you can support me directly through Patreon
  / scottmanley