Extreme?
When we went to the Moon,
something made us come back, break the molds and burn the blueprints.
40 years later the last remaining F-1 engine was disassembled, 3D scanned, reassembled and tested
NASA resurrects its most powerful rocket engine after 40 years, for science! | ExtremeTech
The methane trubo-pump has been tested:
http://www.nasa.gov/centers/marshall...rs-lander.html
22LR ain't rocket science. Here's something to get started:
3D Printable Rocket Nozzles Part 1: The Math | Bill Waters