I shot a Kel-Tec pistol that fired a 5.56 round. Can’t remember the model name, but damn, what a loud gun.
It is call a PLR-16. Uses the same magazines as the M-16 rifle. If SHTF and the WWLAO (world without law and order) one could add an illegal stock to pistol and you have yourself a short PDW (personal defence weapon). There has been some consumer complaints. The weapon is made of polymer and where the bolt goes back and hits the plastic stock/receiver the plastic can start cracking after several thousand rounds of usage. I don’t know if Keltec redesgin and reinforced that vulnerable spot.