To handle this, Gyrojets are spin stabilized — angled rocket nozzles would spin the bullet up to rotational speeds higher than most rifle rounds. While they may sound a bit like child’s toy ...

Ramjet: Ramjets work by accelerating air through a converging-diverging nozzle ... The most basic rockets work by expelling exhaust gases, which push the rocket in the opposite direction.

You don’t think of hobby-grade 3D printing as a good method for creating rocket nozzles. But [Mister Highball] managed to create a copper nozzle using a common printer, a kiln, and some special ...