One of the most neglected aspects of defensive knife training is the skill necessary to actually get your knife into the fight. Just like drawing a handgun, you must be able to draw your knife quickly and reliably in response to a sudden, life-threatening event. However, with a knife — especially a folding pocketknife — things are even more complicated.

With a good handgun draw stroke, you achieve your master grip with the gun still in the holster, you draw the gun, orient the muzzle, and you’re pretty much in business. Obviously, if your gun has a manual safety, you also have to swipe the safety off before you can fire, but the process is still pretty straightforward.

With a folding knife, however, the draw stroke is only half the battle. Once you have the pocketknife in hand, you still have to open the blade to make it a viable weapon. Ideally, you should be able to do that one-handed, so you can simultaneously use your other hand as a guard. That means performing complex motor skills with a sharp object using only one hand—all while experiencing the physiological effects of life-threatening stress. That’s a serious challenge.

High-Speed Folding Knives

Modern folding knives suitable for self-defense typically have some type of feature that allows them to be manually opened one-handed. Usually, this takes the form of a “thumb purchase,” like a blade hole, a thumb stud, or a disk that provides traction for the thumb to pivot the blade into the open position. “Flipper” openers take a different approach, offering a protruding tab near the heel of the edge that is stroked or pushed with the index finger to open the blade. Although all of these can work well, they require a specific grip on the knife and a fair amount of fine motor skill—both of which are difficult to achieve under stress and even harder when your hands are sweaty or you’re wearing gloves.

My interest in high-speed folder deployment began more than 40 years ago when I first started carrying a folding knife for personal defense and training diligently in its use. Since then, I have pressure tested every one-handed deployment method you can imagine. The best balance of speed, reliability, and versatility I’ve found is the inertial opening.

Inertia is formally defined as “a property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless that state is changed by an external force.” In simpler terms, an object that is in motion tends to want to stay in motion. Translating that concept to the blade of a folding knife, if you rotate the closed knife quickly around the blade’s pivot pin, you impart inertia to the blade. If you then stop the movement of the handle and the inertia of the blade is sufficient, the blade will continue to rotate, overcoming any spring force that’s keeping it closed and continuing into the fully open position. Best of all, you never have to hunt for the thumb purchase or touch the blade.

Pocketknife Opening Methods

There are several different inertial opening methods, but the key to all of them is remembering that the blade always pivots on its pivot pin. The closer axis of rotation of the closed knife is to the pivot pin, the more efficiently inertia is applied to the blade and the more readily it opens. Conversely, “wrist snaps” and whip-like motions that center around the elbow, shoulder, or any other axis far from the blade pivot do not impart inertia efficiently to the blade, so they don’t work as well—if at all. You may burn more calories, but your knife won’t open.

My preferred inertial opening starts by drawing the closed knife from your pocket and gripping the handle between your fingertips and thumb. Your fingers should be extended and perpendicular to the handle of the knife and the pivot pin should be even with the top edge of your index finger. Initially, start by holding the knife about a foot in front of your shoulder with your elbow bent about 90 degrees. From this starting position, raise your elbow to the side by rotating your arm at the shoulder joint. Now lower your elbow, again pivoting at the shoulder. Done properly, the knife’s pivot pin should stay in the same basic location in space. Do this movement slowly a number of times and you’ll soon get the feeling that your shoulder and the pivot pin are on the same axis.

Now, maintaining the same form, raise your elbow and then snap it down quickly. Focus on your knife’s pivot pin and make sure it stays in the same spot in space. Done with sufficient speed and the proper axis of rotation, your blade should open. At first, it may open only a little bit, but with practice, it will soon snap all the way open and lock.

Training With a Defensive Knife

To make this technique easier to learn, it helps to start with a knife that has a heavier blade. More blade mass means more inertia and a shorter path to success. Also, the weaker a folder’s detent (the mechanism that holds the blade closed), the easier it is to open. Knives with LinerLocks, Axis Locks, and Compression Locks are significantly easier to inertially open than back locks and frame locks.

Once you can open your knife consistently with this method, integrate the opening with your draw stroke. Make sure you achieve a proper grip as soon as the knife clears your pocket and immediately flow into the inertial opening. As your skills improve, you’ll be able to streamline your movements to open your knife more fluidly, closer to your body, and in a way that doesn’t cause undue wear and tear on its mechanism.

High-speed deployment is a critically important skill if you carry a folding knife for personal defense. The inertial opening is one of the best methods of achieving that skill and mitigating the effects of life-threatening stress.

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