Firing a liquid engine is subject to local fire code. Basically, they are in the same legal category as fireworks. I believe James is right that in the US at least there are no restrictions on making and owning liquid rocket hardware.
Bob On Wed, 27 Aug 2014 04:45:34 -0700"James G" <dmarc-noreply@xxxxxxxxxxxxx> (Redacted sender "d0ch011iday@xxxxxxxxx" for DMARC) wrote:
Date: Tue, 26 Aug 2014 20:34:06 -0400 Subject: [AR] Laws on Liquid Fueled Rocket Engine Construction From: Eric Sims <ericsimsm@xxxxxxxxx> I was wondering what kind of laws pose restriction for liquid fueled engine construction? Thank you -Eric SimsA Liquid fuel rocket engine is just plumbing. Some fuels, esp. at larger quantities have restrictions and hazardous handling requirements, and you are likely to attract the curiosity of various government agencies, but the machinery itself is not restricted the way that firearms are.-James