Can You Stop a Trigger Pull?

Is it possible to stop an action once you begin? Obviously, the answer is yes for some actions, perhaps no for others. Could you stop an involuntary eye-blink in mid blink? Can you stop a trigger pull once you have actually started the pull? Some experimentation I have done recently concerning just how fast one can pull the trigger leads me to believe that once you actually start to pull the trigger, you probably could not stop in mid pull. If true, that has implications for the private citizen involved in a lawful use of deadly force.

Prosecutors have criminally charged police officers when the officer has shot someone in the back or when the officer shot someone falling down, stating that these shots were unjustified. There is a fine line between shots that are a lawful response to a deadly threat and shots that are fired after the deadly threat ceases. The same is true for a private citizen—perhaps more so. Dynamic, deadly encounters can happen very quickly and a private citizen’s use of deadly force in lawful self defense can be over in moments. However, close legal scrutiny on the defender’s decision to start and stop shooting can result in the aftermath taking years to play out.

Research has shown that most people can stop an action that they had just started but have not completed in 200 – 250 milliseconds (see reference #1). However, the ability to stop an action in this timeframe implies that the initial reaction and motor movement to complete the action takes longer than 200 ms to complete. An action that takes less than 200 ms to complete probably cannot be stopped.

So how does this apply to pulling the trigger? Some definitions are in order. When I say pull the trigger, I am describing the action of pressing the trigger and releasing pistol’s sear from one of two positions: beginning from the trigger fully forward at rest or from the trigger finger holding the trigger staged to the rear under tension with no slack—the so called reset position. I am not describing the action of slowly increasing pressure until the sear releases, but rather a rapid, smooth pull starting with no movement of the trigger finger and ending with the pistol firing.

Just how fast does this happen? My recent experiments indicate that it is surprisingly fast—much faster than I initially thought possible. We had four participants in the experiment: Two IDPA 6-gun Masters, one intermediate-level shooter, and one participant who was shooting a pistol for only the 2nd time in their life. The task was straightforward and used one of two starting positions. Position #1 began with the trigger fully forward, trigger finger touching trigger, and no tension on the trigger. The participant pulled the trigger straight to the rear as fast as they could in one smooth motion without pause until the pistol fired. Position #2 began with the trigger staged to the rear so that the trigger had no slack and the shooter felt the sear’s resistance. Shooters could put as much tension as the mechanism allowed without releasing the sear (note: no participant fired an unintentional shot during this process). 

On their own, the shooter pulled the trigger straight to the rear as fast as they could in one smooth motion without pause until the pistol fired. In all of the trials, I used the a SIG P320 with a stock trigger and the a P365 with a stock trigger—the same pistol for each participant. (I tried this previously with different pistols and realized there was a notable difference time-wise between action types, even with striker fired pistols. We used the SIG P320 and P365 to eliminate this variable.)

I measured the time from the first video frame indicating the trigger was moving until the pistol fired. I used a camera running at 240 frames per second (the fastest camera I have) to measure the trigger pull speed. Although 240 fps seems fast, it was clear when I analyzed the data that there was actually movement in this process that was faster than the camera could record. Even so, I think the video was sufficient to measure the action with a reasonable level of accuracy. (a short video and no, that grips is not my normal grip. I modified the grips to ensure I could record the entire trigger movement.)

SIG P320: From position #1 with the trigger fully forward, the average time for all participants to complete the trigger pull with the P320 was 0.0297 seconds. The fastest time was 0.0208 seconds with the slowest being 0.0375 seconds.

From position #2 with the trigger staged to the rear and under tension, the average time for all participants to complete the trigger pull with the P320 was 0.0153 seconds. The fastest time was 0.0083 seconds (several pulls—pretty darn fast) with the slowest being 0.0250 seconds. Initially, I thought that the 0.0083 times were simply too fast to be credible; however, another camera running at 240 fps produced the same result.

SIG P365: From position #1 with the trigger fully forward, the average time for all participants to complete the trigger pull with the P365 was 0.0297 seconds. The fastest time was 0.0083 seconds as well with the slowest being 0.0333 seconds.

From position #2 with the trigger staged to the rear and under tension, the average time for all participants to complete the trigger pull with the P365 was 0.0145 seconds. The fastest time once more was 0.0083 seconds and the slowest was 0.0167 seconds.

When you look at the total data set for each starting position, there really is almost no statistical difference between the skilled and relatively unskilled shooters. Every trigger pull I recorded was significantly faster than 200 ms and this leads me to believe that it would not be possible for the participant to stop the pull once they had started.

What is the implication for the armed citizen? If you are committed to firing a shot and have started to pull the trigger, the speed with which you can pull the trigger likely precludes stopping that action. In 2000 and again in 2009, Bill Lewinski and others studied how fast someone can turn and how fast someone can stop shooting (reference 2 & 3). In the 2000 study they found that the average time for someone to turn in scenarios where the threat was firing at a fictional “police officer” was 0.0300 seconds from one starting position and 0.0900 seconds from another. If the threat turns in the instant you pull the trigger, the trigger pull speed when combined with turning speed (particularly the speed of a young, athletic person) could easily result in shooting the threat in the back.

Given that at any given moment in our lives today we are probably being video recorded, that video recording may show the threat turning away as you fire making it look like you are intentionally shooting them in the back when they are no longer a threat. Knowing trigger pull speeds and the speed in which someone can turn could be very useful information for the defense in case of criminal charges.

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1. On the ability to inhibit simple and choice reaction time responses: a model and a method. G D Logan, W B Cowan, K A Davis; J Exp Psychol Hum Percept Perform. 1984 Apr;10(2):276-91.

2. Why is the Suspect Shot in the Back? Finally, Hard Data on How Fast the Suspect Can Be In 11 Different Shooting Scenarios; Bill Lewinski, Ph.D.; The Police Marksman November/December 2000 pgs. 20-­‐28

3. New Developments in Understanding the Behavioral Science Factors in the “Stop Shooting” Response. Law Enforcement Executive Forum - 2009 9(4) 35; William J. Lewinski, PhD; Christa Redmann, Bethany