I dati e le fonti bisogna vedere cosa intendi.
Noi ci riferiamo a quelli che sono gli input dei nostri responsabili dei corsi Law enforcement (uno dei quali è stato membro di una squadra Swat )e che sono poi condivisi da tutti i poliziotti e militari che vengono ai nostri corsi.
Cmq qui trovi un articolo famoso pubblicato già nel 1983 sulla rivista della Swat:
http://www.theppsc.org/Staff_Views/Tueller/How.Close.htmL'autore ha dato il nome a un drill usato dalla polizia di mezzo mondo.
Qui invece di seguito un articolo pubblicato un paio di anni fa su uno dei forum più famosi in ambito law enforcement da parte di un noto istruttore di tecniche di tiro e simili:
"Don't Bring a Gun to a Knife Fight
by Chris Upchurch, Suarez International Staff Instructor
Mark Twain once said, “It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so.” In training students to defend themselves with a firearm, one of the instructor’s jobs is to disabuse students of certain, widely held but mistaken notions. The idea that shooting someone with a handgun will send them flying across the room, for instance, or that warning shots or shooting to wound are a good idea. One of the most common is encapsulated in the old saying, “don’t bring a knife to a gunfight,” often delivered with an air of smug superiority on the part of the gunman. Implied by this is the idea that the gun is in all ways a superior weapon to the knife, and that a skilled gunman has little to fear from a knife wielding assailant. The problem is it just ain’t so.
The best known effort to get gunmen to take knife armed assailants more seriously is the Tueller Drill. Dennis Tueller was a Salt Lake City police officer. In 1983 he wrote the classic article, “How close is too close?” published in S.W.A.T. Magazine (back when it was a more serious publication than it is today). In the article he pointed out that it took a reasonably skilled gunman about 1.5 seconds to draw his pistol and fire the first shot. In that time a healthy adult male could cover about 21 feet from a standing start. Since then, the “21 foot rule” and drills demonstrating this have become a standard part of training for law enforcement and armed citizens alike. Even in his original article, Tueller pointed out that firing one shot just as the knife wielding maniac reaches you is no guarantee that you won’t get cut. Tueller advocated drawing the gun as soon as the danger clearly exists, rather than based on a particular distance, but some agencies have pushed the magic distance out to 30 feet to provide time for multiple shots and some margin for error.
The 21 foot rule is predicated on stand and deliver type shooting (though Tueller himself encouraged taking a step backwards during your draw to add another three feet of distance). Against an attacker armed with a contact weapon, moving away from the attacker is an obvious solution. Many schools teach backpedaling while you draw and shoot. This works much better on flat smooth ranges than it does in the real world littered with curbs, discarded bottles, cars, etc. Tripping and bouncing the back of your head off the pavement may well leave you unconscious and at the tender mercies of the criminal with the knife. Even if you don’t trip, few of us can outrun someone when we are going backwards and he is going forwards. It is far better to turn, point your toes away from the attacker, and run, shooting twisting your upper body and shooting one handed to bring the gun into action. Using these techniques, students in Suarez International classes can get their gun out and put multiple rounds into the attacker at half the distance Tueller laid down, or even less (depending on the relative athleticism of the student with the knife and the student with the gun).
Defeating the Tueller drill at half the usual distance is quite impressive, but how relevant is any of this to the armed citizen? Remember, Tueller was a police officer. Police are often dispatched to respond to “man with a knife” calls, requiring them to approach and interact with a knife wielding individual. They may spot this individual well beyond 21 feet. Tueller’s article was an attempt to persuade fellow officers that they needed to get their guns out even when the person they were approaching “only” had a knife.
I don’t carry a badge, and I’m not paid to approach disturbed individuals armed with knives. A much more realistic threat from my perspective is someone with a knife who is willing to threaten to kill me over the contents of my wallet. This kind of situation is unlikely to unfold from 21 feet, or ten feet for that matter. Imagine a mugger seven yards distant yelling, “You! Over there! Give me your wallet or I’ll come over there and stab you!” The very idea is laughable. A criminal intent on using a knife to extract money from someone isn’t going to tip his hand at 21 feet. He’s going to get within arm’s reach before revealing the knife. Ideally, we would be sufficiently aware to realize his intent before he gets that close and take measures to evade, but sometimes our awareness fails, or criminals are clever, leaving us to face an adversary with a knife at close range. The reality of a knife attack is probably going to be 21 inches, not 21 feet.
Many gun schools don’t address knife attacks in this realm at all. Those that do often teach the speed rock, or some other variant of retention shooting. The details vary from school to school, but most involve fending off the knife with the support hand while you draw and shoot from retention with the primary hand. This works well when the attacker is a paper target, but it just doesn’t hold up in force on force. One arm just isn’t sufficient to hold off a determined attacker with a knife. He can get in several good stabs with the knife before you get your gun into action, and even after you do, you’re just trading pistol wounds for knife wounds. If he realizes you’re going for a gun, he can even use his support hand to foul your draw, in which case you may never get that gun into action.
The problem with speed rock-type techniques is they try to do two things at once and end up doing both of them badly. Fending off a knife wielding attacker is a job that demands your full attention and both hands. As long as the attacker is within arm’s reach, this is a hand to hand problem; the gun in your holster is irrelevant at this point. The immediate priority is to keep his knife out of your innards. Once you’ve blocked or parried the initial attack, the next objective is to create enough time and distance to get your gun out and get hits on the attacker (about 2 seconds and 2 yards). Depending on your level of awareness and the strength of the initial attack, it may be possible to do this simultaneously with the initial parry by launching a simultaneous palm strike to the opponent’s face and moving explosively off the line of attack. If the attacker’s energy level is higher, it may take both hands and a solid platform to stop the initial stab. If you’re surprised by his attack, all you may be able to do is throw a block out towards the incoming blur of the attack. In these cases, you may need to block one or more additional attacks before you’re ahead of the curve enough to get off line and gain distance. Once you’ve created that distance, then it's time to turn this from a knife fight into a gunfight.
At the arm’s length distances where real knife attacks happen, having a gun does not put you in a position of superiority. In fact, going directly for your gun can be an invitation for him to stab the hell out of you. Initially, at least, close range knife attacks are a hand to hand problem. As long as he's within arms reach the saying should really be, “don’t bring a gun to a knife fight.”
Discuss the reality of a knife attack on Warriortalk. Learn how to win these kinds of fights in Zero to Five Feet Pistol Gunfighting.
Qui una spiegazione sulla corretta interpretazione della distanza di sicurezza e la sua evoluzione:
http://www.policeone.com/edged-weapons/articles/102828-Edged-Weapon-Defense-Is-or-was-the-21-foot-rule-valid-Part-1/