For 80 years, give or take a decade, the double-action (DA) revolver was the premier self-defense sidearm in the U.S., for law enforcement and private citizens alike.
The entire idea behind the DA wheelgun was that, in a hurried, reactive situation the revolver could be drawn and fired instantly in double-action mode (the name derived from the fact that the trigger performed the double actions of cocking the firearm and firing it). However, if a more precise or difficult shot were needed, then the shooter could cock the hammer with their thumb and take advantage of the lighter single-action trigger pull.
Of course, people being lazy, most didn’t use the double-action pull at the range when shooting for practice or fun, since the single-action pull was easier to hit with, and people like easy.
Toward the end of the revolver’s days as the main police duty sidearm, Smith & Wesson had a dominant market position. Accordingly, as the transition to semi-automatic pistols accelerated through the ’80s, a lot of departments switched to Smith & Wesson’s offerings thereof.
These semi-auto pistols had a trigger similar to the revolvers they replaced in that they had both double- and single-action pulls. The difference was that, after firing the gun with the initial double-action pull, the pistol would cock itself and subsequent trigger pulls would be single action. At the end of a string of fire, applying the safety would safely lower the hammer and allow the pistol to be reholstered.
But, people still didn’t much like to practice—they would still thumb-cock the pistol to avoid the double-action pull. Older instructors called these handguns “crunchentickers,” and some even advocated the practice of “shot-cocking,” or hurriedly throwing away the first shot to land God-knows-where in order to get to that lighter single-action pull as fast as possible. Further, people would avoid practicing routinely decocking the piece and then try and holster a cocked gun with predictably noisy results.
The initial response to this was double-action-only semi-autos that simply didn’t allow the hammer to be cocked. Each shot was that longer and heavier double-action pull that gave people the maximum opportunity to pull the sights off target during the trigger’s considerable travel.
Various manufacturers attempted to offer solutions to that problem. Heckler & Koch and SIG Sauer offered systems that, while mechanically different, were functionally pretty similar. Heckler & Koch called its the “LEM,” for “Law Enforcement Module,” and SIG’s was the DAK, an abbreviation for “Double Action Kellerman.” These systems both used the cycling of the slide to partially tension the action, so that while each trigger pull was long like that of a true double-action, it was much lighter.
Smith & Wesson’s answer to the DAO conundrum differed slightly. While it, too, made use of the slide cycling to pre-load the action, with the Smith & Wesson it was the trigger travel that was shortened while the weight was still heavier than a single-action pull.
The problem with all of these designs was that they made the guns easier to shoot than the regular DAO for the average end user—but they penalized the people who had been actually diligently practicing their trigger pulls with dry-fire routines. With the old revolvers, DA or true DAO semi-autos, the self-resetting trigger was practically tailor made for dry-fire practice, but these guns had to be manually reset to get the proper press. And mastering a long, heavy trigger pull does not happen without rather a lot of practice.
With the rise of the striker-fired pistol, epitomized by the standard-bearer of the type, the Glock, came the easy-to-shoot gun that seemed to be the ideal compromise solution.
The trigger pull could be just heavy enough to keep lawyers happy and yet had a short enough travel to make it reasonably easy to shoot adequately with a minimum of practice. There was no safety to forget to take off, like there would be with a single-action semi-automatic, and no decocker to remember to use before holstering, like a traditional double action.
It wasn’t without its downsides, of course. A gun that’s easy to fire on purpose is going to be relatively easier to unintentionally discharge, too. The (comparatively) shorter and lighter trigger is easier to negligently crank off a round while “woobie checking,” which is the unconscious habit of the trigger finger to wander into the trigger guard, as though seeking reassurance the trigger is still there. You’ll see this a lot in videos of force-on-force tactical training or footage of actual police incidents.
Bring this up as a factor, or the problem of the shorter trigger pull while holstering, and the most rabid Glock fans will counter “Well, that’s just a training issue!” Hey, so is not being able to hit with a double-action trigger. Pick your poison and practice, practice, practice.