definition of single action / double action

[G.C.Montgomery]

Now what's really going to bake your brain is reading Farnam's descriptions of no less than seven handgun operating systems. And as Skiprr noted...The lines have become blurred with the advent of designs like the Walther P99 and Springfield Armory's XD.


While we're on the subject of operating systems, does HK's squeeze-cocker (P7) count as a single-action, double action or something else? And about the HK LEM or ParaOrd LDA...Are these really double-action pistols since only part of the hammer is cocked by the slide but the part we can see is still at rest?

[Liberty]

That's not entirely correct on the Glock. The difference between the action of the Glock and an XD is that the Glock's striker assembly is under little to no tension at rest.

Very good description. I hope it doesn't strike (pun intended) fear into those folks trying to understand SA versus DA in an age where the mechanisms have distinctly blurred. But your description is precisely why, if shooting IDPA, a Glock is allowed in the Stock Service Pistol division, but a comparable XD isn't.

John Farnam's thought on the matter is: "The two terms, double- and single-action, are so muddled that they have now become inexplicit and virtually useless for the purpose of any accurate description of an autoloading handgun operating system. The terms are still useful only in differentiating revolver types."

While He has a valid point for some guns, I dont think there is much confusion until you take the hammer away. If I describe my hammer operating gun, and I tell someone its a DA/SA there isn't much room for imagination on how it works.

[CompVest]

+1

[AggieBonz02]

I'll stir the pot a little bit more.

If you want to simply classify handguns as SA or DA, then from the simplest description, you get:

SA - Performs only one action (i.e. causing the firing pin to punch the primer within the cartridge). Another way to look at this is it is releasing the potential energy stored in the springs that make up the firing mechanism.
DA - Performs two actions, with a necessary one being the same action of a SA. The other action is one that applies energy to the spring within the firing mechanism (i.e. cocking the hammer or striker). IMO, true DA handguns have what is called a "restrike capability" - that is the ability to pull the trigger and have the firearm perform both actions repeatedly.

Obviously there are handguns that perform a combination of the above - those being DA/SA, DAO, Safe Action, and the like. To further complicate and distort the initial simplicity of this concept, many of them fall in between because they are not true DA or SA handguns.