The Evolution of Different Trigger Types

The Evolution of Different Trigger Types

In my office, I had the duty gun belts I’d worn over the years hanging vertically on a wall. They were in chronological order.

The display was trapezoidal. It was level across the top, but slanted on the bottom. For some reason, the gun belts got longer as I got older.

This Category is about different types of triggers on “duty” pistols I have carried, especially the Double Actions (DAs):

  • Double / Singles (DA/SAs)
  • Double to Singles (DA->SAs, or DA to SAs)
  • Double Action Only (DAOs), and
  • Double Action Kellerman (DAKs)

. . . along with some lessons I have learned about them along the way.

But first, in this article, we’ll cover how we got to where we are.

If you’re reading this, you probably already know that Single Action means the trigger only does one thing: releasing a cocked hammer to fall. SA Only pistols must be thumb cocked before each shot.

Double Action means trigger cocking. In Double Action mode, the trigger both cocks and releases the hammer. If the hammer has already been cocked manually, pulling the trigger performs only the one (Single) action of releasing the hammer to fall upon the primer, making gun go boom.

Historical Development: Double / Single Action Revolvers


In the ye olde days of the 1800s, most revolvers were Single Action Only. When you thumb cocked for the next shot, the cylinder would rotate one position, till the next round was directly behind the barrel.

While this enabled the hammer to be kept “safely” down (as long as it was over an empty chamber in those days, since the firing pin protruded through the breech face when the hammer was down), it did require an extra step each time you needed to send lead downrange fast.


Double Action revolvers were around as early as early as 1851, when Deane-Adams produced a Double Action Only; it could not be thumb cocked for Single Action fire. An English concern, Beaumont, produced what Jeff Cooper called a Selective Double Action (capable of DA trigger cocking OR SA thumb cocking) a few years later. Smith & Wesson and Colt started producing selective DA / SAs in 1877.

DAs were popular on pocket pistols, but SAs, like the ubiquitous Colt Single Action Army, were standard for duty carry in the 1800s. There were exceptions. “Billy the Kid” (William Bonney) used a brace of DA / SA Colt .41 Lightnings.

The Smith & Wesson Model 1899

Significant for its effect on subsequent US Military pistol calibers and development, at the end of the 19th century the US Army (and Navy) adopted the Smith and Wesson Model 1899 Double Action revolver, very similar to the Smith revolvers I was issued 80 years later.

It was supposed to reduce the need for training, as the cartridge (.38 Colt) had far less recoil than the .45s and .44s standard in previously issued Single Actions, and of course, with a DA, one need only point, pull and pray, right? No need for that extra cocking step, which might be overlooked in moments of necessary haste.

The Army (or at least, its officers) took the Model 1899 to the Pilippines during our counterinsurgency there from 1899 to 1902. One may justifiably assume that the DA option was a boon in the Philippines. Having patrolled in head-high elephant grass in the Rio Grande Valley, I have some inkling that when US patrols were ambushed in similar undergrowth (in the PI, or later, Vietnam), the ranges were very close.

Even if it were not tropical, the vast majority of the Philippine insurgents were armed primarily with bolo knives, a close range weapon. The ambush of Company C, 9th US Infantry, as they ate breakfast in the open in the town of Balangiga on the island of Samar, took place primarily with bolos. That’s DA range for sure, even though those officers most likely practiced and qualified shooting SA at distance on marksmanship based courses. Most of the 74 man garrison was annihilated.

The .38 Colt cartridge of the S&W M1899 was a disappointment. Over and over we read of Philippine insurgents being shot, but continuing to attack until they had sunk their bolo deep into somebody.

Filipino bolo (top) with a Spanish M1941 bayonet (bottom) for size comparison. Some bolos were larger.

We might expect a zombie-like indestructibility on the part of the Moros, one of the many cultures in the Philippine archipelago; the Moros were devout Muslims whose ticket to Paradise was dying bathed in the blood of infidels. But many, if not most, of the insurgents were nationalists, rather than religious fanatics. They just wanted us gone, as they had wanted the Spaniards gone.

In fairness to the M1899, many more insurgents were shot by .30 Krags and .45/70 Springfields and still kept coming, perhaps driven by necessity–they had to keep getting closer to use their bolos. But the lackluster stopping power of the .38 Colt revolver cartridge during the Philippine insurrection led directly to the adoption of the .45 ACP cartridge for the M1911 auto pistol.

The development of the .45 ACP cartridge is a fascinating story that has been told elsewhere.


At the turn of the 20th century, most militaries adopted semi-auto pistols.

The US adopted a Browning-designed .45 pistol in 1911. But when the US stopped sitting on the fence in 1917, sending troops to France to fight the Germans, there weren’t enough M1911s for our Expeditionary Forces.

Pre-existing Colt and Smith & Wesson large frame DA / SA revolvers, previously chambered in .45 long colt (a longer, rimmed cartridge) were re-chambered for the military standard .45 ACP (a fat, stubby rimless cartridge). Both the Smith and the Colt were designated M1917.

Colt M1917 with Tyler’s T-grip adapter (upper right), compared with a modern Ruger SP101 (lower left). Zip strip has .38s for the SP-101; full moon clip (upper left) has .45 ACPs for the M1917. They used half-moon clips in WWI.

Fun fact: Colt revolver cylinders rotate clockwise from the rear; Smiths and Rugers counter-clockwise.

American law enforcement officers (LEOs) carried DA / SA revolvers through the 1980s. So did the US Air Force.

The Smiths discusses lessons learned during my USAF revolver education.


Selected Sources

“Jeff” Cooper and Kenneth M. Bayless, Fighting Handguns (Trend Books, 1958)

Col Arcadi Gluckman, US Army (ret), United States Martial Pistols and Revolvers (Bonanza Books, 1956)

Brian McAllister Linn, The Philippine War 1899 – 1902 (University Press of Kansas, 2000)

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