Well first off you will notice that the chamber doesn't actually have any bullets in it. It's more likely that it has an energy cartridge and happens to be designed like an old school revolver for nostalgia purposes. Almost all of the weapons fire some sort of energy vs actual bullets. Either way I guess an advanced civilization that has mastered space flight and the ability to deconstruct and reconstruct physical items wouldn't be able to create a weapon that differs from those used before the golden age.