Explain in detail the difference between firearm single-action and double-action

Dear bitseeker-ga;

Thank you for allowing me to answer your interesting question.

A single action firearm has to be cocked each time before it can be
fired. In most models this is necessary because only one cartridge at
a time can be loaded into the firing position. Re-cocking the weapon
after firing it manually brings a new cartridge into the firing
position (and in come models ejects the used cartridge).

A double action firearm can be fired over and over again in rapid
succession as quickly as the trigger is pulled. The reason this is
possible is because ?the action? or movement of the cylinder performs
two functions (the ?double action?): it (1) serves to move the spent
cartridge out of the way and moves the new cartridge into firing
position, and (2) it re-cocks the firearm for another shot in rapid
succession.

I hope you find that my research exceeds your expectations. If you
have any questions about my research please post a clarification
request prior to rating the answer. Otherwise I welcome your rating
and your final comments and I look forward to working with you again
in the near future. Thank you for bringing your question to us.

Best regards;
Tutuzdad-ga ? Google Answers Researcher



INFORMATION SOURCES

F.R.&I.
http://www.f-r-i.com/women/revs.htm

GUN SAFETY PAGE
http://www.gilawilderness.com/sportspg/gunsafety.htm


SEARCH STRATEGY


SEARCH ENGINE USED:

Google ://www.google.com


SEARCH TERMS USED:

Single action

Double action

Firearm

Difference

bitseeker,
I happened across this answer a couple weeks ago and I cant get over
the feeling that it is not totally correct as stated.  It's been a
couple of years since I was into shooting, but here is my
understanding of double vs. single action:

The action refers to the effect of the trigger on the hammer.  With
double action, pulling the trigger has 2 actions.  First it cocks the
hammer or pulls it back.  Second, it releases the hammer to fire the
weapon.  With single action the hammer must be cocked before the
trigger is pulled.  Pulling the trigger has only one action -
releasing a cocked trigger.

Most revolvers are double action and most semi-automatics are single
action (though some are double action on the first shot).  I followed
the links that Tutuzdad has given and notice a discussion on single
action revolvers.  I have never seen a single action revolver, but the
discussion on that page refers to the fact that the hammer must be
manually cocked before firing.  A semi-automatic is generally cocked
by pulling back the slide and can then be fired in a single action
mode.  Each firing of the gun causes the slide to go back to re-cock
the hammer and additionally to eject the spent cartridge.  Many
semi-automatic handguns have external hammers and the ability to
de-cock the weapon.  I believe (been a long time) that some must be
manually cocked at that point and I know that some also work in a
double action mode for the first shot if the hammer has been
de-cocked.  There are some semi-autos that have no external hammer and
because of the internal action are considered double action on each
shot - i.e. the Glocks.

What does all this matter for the shooter?  Well generally, Glocks
excluded, the trigger pull in the double action mode is much harder
and more difficult to keep steady during the full shooting practice. 
Many weapons in the single action mode are very sensitive and require
a very little trigger pressure to discharge.

Hope this helps.

passtechgroup

The answer given is incomplete.

As passtechgroup states, single and double action refer to the
trigger. A double action both cocks the hammer and allows it to fall,
thus firing the gun.  A single action only allows it to fall, so
something else has to cock the hammer before the gun can be fired. 
Please note that not all guns have hammers, but we'll use the term
throughout this discussion for simplicity.

It gets confusing because the result of this means different things in
different types of handguns.  Note that these terms are not usually
applied to rifles and shotguns, which overwhelmingly have single
action triggers.

In single action revolvers (what tutuzdad incorrectly referred to as
"single action firearm"), the shooter has to manually cock the hammer
for each shot.  Most of the cowboy guns of the old west are of this
type, most notably the Colt Model 1873 "Peacemaker."  This gun type is
obsolete technically, but the nostalgia factor means that there are
still tens of thousands of this type of gun made every year.

Double action revolvers - like Dirty Harry's Smith & Wesson .44 Magnum
- can be fired by just pulling the trigger, no need to manually cock
the hammer.  However, it gets confusing because double action
revolvers can actually be fired single or double action.  That is, you
can either simply pull the trigger to fire (double action) or manually
cock the hammer and then pull the trigger (single action).  The single
action capability is retained because it means a much lighter and
shorter trigger pull.  A double action pull will typically require
around 12-16 pounds of presure, while a single action pull might be
3-6 pounds.   Hunters and some types of target shooters typically
prefer to shoot in single action mode because the lighter trigger pull
is an accuracy aid.  On the other hand, police departments that still
use revolvers and individuals who use them for self defense almost
never use single action mode, since in the stress of an encounter it
is all too easy to put a few pounds of pressure on the trigger and
thus inadvertently fire the gun.  In fact some revolvers meant for
police or self-defense use have the single action mode disabled (i.e.
they cannot be manually cocked) to ensure that any trigger pull is
deliberate.

Now we move to semi-automatic handguns, aka pistols.

First up are the single actions.  The most famous of these is the old
standard US military sidearm, the Colt Model 1911, other include the
Walther PPK and Browning Hi-Power.  Single action again means that
that the trigger does not cock the hammer, so it has to be manually
cocked before taking the first shot.  However, after the first shot
the movement of parts other than the trigger (usually the slide)
automatically cocks the hammer.  So unlike a single action revolver,
for shots after the first one, a single action pistol will fire every
time the trigger is pulled without the shooter having to touch the
hammer.

A double action pistol - such as current the U.S. military sidearm,
the Beretta Model 92 and others like the H&K USP or Ruger P series -
differs from the single action only in that it does not need to be
cocked for the first shot.  For the first shot, the trigger will both
cock the gun and fire it, in subsequent shots, the slide will
automatically recock.  This means that the trigger pull lightens up
considerably after the first shot, which has once again led some
gunmakers to offer a "double action only" version that does not
automatically cock the hammer so every trigger pull requires
noticeable effort.

The term "single action firearm" that I used in my answer is
absolutely correct. Revolvers are not the only single action weapons
made, therefore the term "single action firearm" is an appropriate
catch-all phrease for all guns that are of "single action" design. The
additional information offered doesn't add significantly to the answer
given (which happens to be correct and complete for the question
asked).

tutuzdad-ga

tutuzdad-ga.  THe following statements are misleading:

"A single action firearm has to be cocked each time before it can be
fired."

Only single-action revolvers have to manually cocked each time. 
Single action pistols (semi-automatic handguns) only have to be cocked
manually before the first shot.  The action of the slide automatically
recocks them for additional shots.  So technically, yes, they have to
be cocked before every shot, but the shooter doesn't have to do it.

"A double action firearm can be fired over and over again in rapid
succession as quickly as the trigger is pulled."

This is equally true of single action pistols.  After the hammer is
initially cocked, a single action pistol "can be fired over and over
again in rapid
succession as quickly as the trigger is pulled".

"The reason this is possible is because ?the action? or movement of
the cylinder performs two functions (the ?double action?): it (1)
serves to move the spent cartridge out of the way and moves the new
cartridge into firing
position, and (2) it re-cocks the firearm for another shot in rapid
succession."

This only applies to double action revolvers, not pistols
(semi-autos).  In pistols, the trigger has nothing to do with the
movement of cartridges.  It merely trips the sear in single actions
and cocks and trips the sear in double actions, the force of the
recoil or the movement of high speed gases (along with various
springs) do the work of ejecting the spent cartridge and loading a new
cartridge into the chamber.

"The additional information offered doesn't add significantly to the answer
given (which happens to be correct and complete for the question asked)."

Your answer was in no way complete and correct for the question asked.
 Your answer only covered revolvers.  In this case there is a very
real difference in the use of the terms single action and double
action when applied to pistols versus revolvers.