How powerful is the spring action on an OTF switchblade?

I used to collect OTF switchblades and was well networked with other collectors, who were a diverse group including everyone from Navy SEALS (who were issued the HALO series), police officers (who favored the Ultratech series), and ruffians like truckers and bikers (who favored Daltons). This question came up every now and then and has been tested repeatedly.
According to legend, “If you press an OTF switchblade against someone’s back and push the button, you can stab them without even moving your arm!” Unfortunately, this is completely untrue.
Most OTFs are “double action,” which means you slide the actuator switch forward and the blade snaps out… and when you slide the switch back the blade retracts. This is an Italian design from the 1940s which was marketed as a “safety knife” which could be used with one hand with no risk of accidentally cutting oneself. The blade is very lightweight and the mechanism relies on a pair of thin copper springs which stretch as another snaps back. The blade is locked into position with a delicate copper tab which is easily bent and broke were you to stab it into a tree or something. That is your most common OTF found at flea markets and such. The “Concorde” and “Lightning” are some of the better known examples.
Microtech improved this design by strengthening it with better materials, additional springs, and a metal locking block instead of a thin tab. Pirahna uses similar principals. These knives typically start at $300 and go up to about $500 for a standard commercial version… customs and limited runs can retail at over a thousand dollars each.
I have owned numerous Microtechs: 1 Trodoon, 2 Ultratechs, and 5 Combat Trodoons. Best OTF knives ever made. If you hold a piece of printer paper in front of the hole and slide the actuator forward, it will probably penetrate it but the blade will fail to lock and will slide loosely in its track until pulled firmly into the open and locked position. If you hold 2 pieces of paper together, it is unlikely to penetrate at all. This has a similar effect on human flesh. With the hole nearly 3″ away from one’s hand (permitting maximum velocity to be reached), a razor sharp blade ground from Elmax supersteel will penetrate human flesh approximately .25″ then will fail to lock into position. Held against flesh at contact range it is unlikely to break the skin.
Now, that brings us to the most powerful OTF design… The “single action” which utilizes a far stronger spring to launch the blade open. Then, the same button is pressed to unlock it while the other hand pulls a lever, cord, or charging handle to manually retract it. These are heavy duty knives designed not to fail in adverse environments. I have owned a Microtech HALO II, a Dalton Cupid, and a Dalton SOF Millenium. These will pop right through several sheets of paper… but will generally fail to lock open. This also applies to flesh. It will break the skin, and may even penetrate nearly a full inch into soft tissue before failing to lock, but spring action alone will never allow it to penetrate deeper or break through bone.
Either type of OTF can penetrate deeply once fully deployed and locked… just like any other lockblade folder or a restaurant steak knife. The OTF feature, while appearing unduly menacing in a variety of Hollywood films, is actually a safety feature and makes the knife less suitable as a weapon. In addition to failing to lock open if deployment is blocked, stabbing a person will introduce blood to the internal mechanism, which will gum up the works. You cannot just flush it out with WD40 either… these knives require powdered graphite for lubrication. Oil gums them up too, and cellophane tape (from opening packages) sticking to the blade will jam the mechanism badly. Special tools are required to remove these screws for disassembly and cleaning, which voids the warranty. These are precision instruments intended for light duty… the single action versions are more durable, but still far less so than a fixed blade knife.
The power of the OTF varies based upon size and strength of the springs used. Some have experimented with multiple springs or non-traditional mechanisms, but all commercial “double action” OTFs in the $30-$75 price range are very similar, with those in the $150-$300 range being a step up. With single-actions, anything under $50 is garbage from China, with $150 Paragons and $300 Daltons being the industry standard, and the $500 HALO series being in a class of its own… but none are particularly powerful knives.
For “power” you’d need a very long wide handle, containing a spring which requires 2 hands and over 100# of pressure to compress. I have heard stories about such knives being made in Mexico during the 1950s which required the user to press the point against a wall or floor and use their body weight to compress it, but that is unlikely as no example has ever been produced or even referred to in any of the collector forums. The “Pilum” knife issued to Spetsnaz during the early 1980s is the only example of such a powerful spring being used in a knife, but that was a “ballistic knife” similar to a speargun, not an OTF. It would sink to the hilt in a target 10 feer away and could penetrate wood or bone… which is why it is a felony to possess one in all 50 states.
C. R. Jahn, author of FTW Self Defense

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