Bing is your friend... RSMO 571.020
http://www.moga.mo.gov/mostatutes/stathtml/57100000201.HTML
571.020. 1. A person commits a crime if such person knowingly possesses, manufactures, transports, repairs, or sells:
SNIP
(6) Any of the following in violation of federal law:
(a) A machine gun;
(b) A short-barreled rifle or shotgun;
(c) A firearm silencer; or
(d) A switchblade knife.
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This means that as far as the STATE is concerned, if it doesn't violate federal law, you are gtg. HOWEVER, knives are not preempted the way firearms are. This means that a local city, town, municipality may have more restrictive laws. One example is Kirkwood which has a blade length restriction around 2.3" I believe. The way the knife operates is irrelevant if the blade length is "excessive".