eli5 Why weren’t machine guns possible to make in the past?

Question

What stopped 18-19th century armies with guns from being able to create automatic weapons like AK-47s and Uzis?
Since they don’t use electricity I feel like they’re made with materials and technology that was already available in the 1750s, surely they could’ve put their heads together to create a machine gun and just annihilate any ops…

Thanks

In: Engineering

Answer 1

Black powder. Its foul. It creates a thin coating of wet grease that hardens as it cools. It can get thick enough in just a few shots that it literally makes the barrel of a smoothbore musket smaller, and it fills the rifling grooves of rifles to an extent that makes the rifling useless until its cleaned.

Now imagine all that shit inside the receiver of an AR15. Just a few shots will gunk it up and foul the moving parts on the inside. It’ll jam the feed from the magazine, interfere with the gas cycling system, and pretty much destroy its ability to function unless its continually cleaned.