The names of Roman months originally functioned as adjectives (e.g., the January kalends occur in the January month) before being treated as substantive nouns in their own right (e.g., the kalends of January occur in January). Some of their etymologies are well-established: January and March honor the gods Janus and Mars; July and August honor the dictator Julius Caesar and his successor, the emperor Augustus; and the months Quintilis, Sextilis, September, October, November, and December are archaic adjectives formed from the ordinal numbers from 5 to 10, their position in the calendar when it began around the spring equinox in March. Others are uncertain. February may derive from the Februa festival or its eponymous februa ("purifications, expiatory offerings"), whose name may be either Sabine or preserve an archaic word for sulphuric. April may relate to the Etruscan goddess Apru or the verb aperire ("to open"). May and June may honor Maia and Juno or derive from archaic terms for "senior" and "junior". A few emperors attempted to add themselves to the calendar after Augustus, but without enduring success.
In classical Latin, the days of each month were usually reckoned as:
Dates after the ides count forward to the kalends of the next month and are expressed as such. For example, March 19 was expressed as "the 14th day before the April Kalends" (a.d. XIV Kal. Apr.), without a mention of March itself. The day after a kalends, nones, or ides was also often expressed as the "day after" (postridie) owing to their special status as particularly unlucky "black days".
The anomalous status of the new 31-day months under the Julian calendar was an effect of Caesar's desire to avoid affecting the festivals tied to the nones and ides of various months. Because the dates at the ends of the month all counted forward to the next kalends, however, they were all shifted by one or two days by the change. This created confusion with regard to certain anniversaries. For instance, Augustus's birthday on the 23rd day of September was a.d. VIII Kal. Oct. in the old calendar but a.d. IX Kal. Oct. under the new system. The ambiguity caused honorary festivals to be held on either or both dates.
A revolver works by having several firing chambers arranged in a circle in a cylindrical block that are brought into alignment with the firing mechanism and barrel one at a time. In contrast, other repeating firearms, such as bolt-action, lever-action, pump-action, and semi-automatic, have a single firing chamber and a mechanism to load and extract cartridges into it.
A single-action revolver requires the hammer to be pulled back by hand before each shot, which also revolves the cylinder. This leaves the trigger with just one "single action" left to perform - releasing the hammer to fire the shot - so the force and distance required to pull the trigger can be minimal. In contrast, with a self-cocking revolver, one long squeeze of the trigger pulls back the hammer and revolves the cylinder, then finally fires the shot. They can generally be fired faster than a single-action, but with reduced accuracy in the hands of most shooters.
Most modern revolvers are "traditional double-action", which means they may operate either in single-action or self-cocking mode. The accepted meaning of "double-action" has, confusingly, come to be the same as "self-cocking", so modern revolvers that cannot be pre-cocked are called "double-action-only". These are intended for concealed carry, because the hammer of a traditional design is prone to snagging on clothes when drawn. Most revolvers do not come with accessory rails, which are used for mounting lights and lasers, except for the Smith & Wesson M&P R8 (.357 Magnum), Smith & Wesson Model 325 Thunder Ranch (.45 ACP), and all versions of the Chiappa Rhino (.357 Magnum, 919mm, .40 S&W, or 921mm) except for the 2" model, respectively. However, certain revolvers, such as the Taurus Judge and Charter Arms revolvers, can be fitted with accessory rails.
Most commonly, such revolvers have 5 or 6 chambers, hence the common names of "six-gun" or "six-shooter". However, some revolvers have 7, 8, 9, or 10 chambers, often depending on the caliber, and at least one revolver has 12 chambers (the US Fire Arms Model 12/22). Each chamber has to be reloaded manually, which makes reloading a revolver a much slower procedure than reloading a semi-automatic pistol.
Compared to autoloading handguns, a revolver is often much simpler to operate and may have greater reliability. For example, should a semiautomatic pistol fail to fire, clearing the chamber requires manually cycling the action to remove the errant round, as cycling the action normally depends on the energy of a cartridge firing. With a revolver, this is not necessary as none of the energy for cycling the revolver comes from the firing of the cartridge, but is supplied by the user either through cocking the hammer or, in a double-action design, by just squeezing the trigger. Another significant advantage of revolvers is superior ergonomics, particularly for users with small hands. A revolver's grip does not hold a magazine, and it can be designed or customized much more than the grip of a typical semi-automatic. Partially because of these reasons, revolvers still hold significant market share as concealed carry and home-defense weapons.
A revolver can be kept loaded and ready to fire without fatiguing any springs and is not very dependent on lubrication for proper firing. Additionally, in the case of double-action-only revolvers there is no risk of accidental discharge from dropping alone, as the hammer is cocked by the trigger pull. However, the revolver's clockwork-like internal parts are relatively delicate and can become misaligned after a severe impact, and its revolving cylinder can become jammed by excessive dirt or debris.
Over the long period of development of the revolver, many calibers have been used. Some of these have proved more durable during periods of standardization and some have entered general public awareness. Among these are the .22 rimfire, a caliber popular for target shooting and teaching novice shooters; .38 Special and .357 Magnum, known for police use; the .44 Magnum, famous from Clint Eastwood's "Dirty Harry" films; and the .45 Colt, used in the Colt revolver of the Wild West. Introduced in 2003, the Smith & Wesson Model 500 is one of the most powerful revolvers, utilizing the .500 S&W Magnum cartridge.
Because the rounds in a revolver are headspaced on the rim, some revolvers are capable of chambering more than one type of ammunition. The .44 Magnum round will chamber the shorter .44 Special and shorter .44 Colt, likewise the .357 Magnum will safely chamber .38 Special and .38 Short Colt. In 1996 a revolver known as the Medusa M47 was made that could chamber 25 different cartridges with bullet diameters between .355" and .357".
Revolver technology lives on in other weapons used by the military. Some autocannons and grenade launchers use mechanisms similar to revolvers, and some riot shotguns use spring-loaded cylinders holding up to 12 rounds. In addition to serving as backup guns, revolvers still fill the specialized niche role as a shield gun; law enforcement personnel using a "bulletproof" ballistic shield (Gun shield) sometimes opt for a revolver instead of a self-loading pistol, because the slide of a pistol may strike the front of the shield when fired. Revolvers do not suffer from this disadvantage. A second revolver may be secured behind the shield to provide a quick means of continuity of fire. Many police also still use revolvers as their duty weapon due to their relative mechanical simplicity and user friendliness.
With the advancement of technology and design in 2010 major revolver manufacturers are coming out with polymer frame revolvers like the Ruger LCR, Smith & Wesson Bodyguard 38, and Taurus Protector Polymer. The new innovative design incorporates advanced polymer technology that lowers weight significantly, helps absorbs recoil, and strong enough to handle +P and .357 Magnum loads. The polymer is only used on the lower frame and joined to a metal alloy upper frame, barrel, and cylinder. Polymer technology is considered one of the major advancements in revolver history because the frame has always been metal alloy and mostly one piece frame design.
Another recent development in revolver technology is the Rhino, a revolver introduced by Italian manufacturer Chiappa in 2009 and first sold in the U.S. in 2010. The Rhino, built with the U.S. concealed carry market in mind, is designed so that the bullet fires from the bottom chamber of the cylinder instead of the top chamber as in standard revolvers. This is intended to reduce muzzle flip, allowing for faster and more accurate repeat shots. In addition, the cylinder cross-section is hexagonal instead of circular, further reducing the weapon's profile.