Staff Writer (Updated: 5/9/2016):
NOTE: The Carcano Modello 1891 is often (and incorrectly) identified generically as the "Mannlicher-Carcano" rifle. This is in reference to the weapon's origin laying in a Mauser-based Austro-Hungarian rifle design by Ferdinand von Mannlicher (it is noteworthy that many bolt-action rifles of the period utilized the excellent German Mauser action). Another known generic designation for the Model 1891 is as the "Mannlicher-Paravicino-Carcano".
Having developed the new 6.5x52mm Mannlicher-Carcano cartridge, the Italians went to work on a rifle to support it. This led to Carcano modifying the basic Mannlicher design with reworked internals which included a turn-down bolt-handle that was set well-ahead along the receiver. Carcano developed a safety mechanism added to the bolt sleeve. One of the major qualities of the Mannlicher retained was the Mannlicher-patented clip-loaded internal magazine facility. Clip-loaded ammunition allowed the operator to quickly reload his weapon by way of prefabricated "chargers" containing cartridges set at their base along a "clip". While doing away with the need of having the operator load cartridges individually, the function suffered from not allowing the operator to "top off" a partially full magazine. However, the faster reloading process proved this fault negligible.
The base Modello 1891 pattern rifles issued to the Italian Army featured full-length wooden stocks with an integrated pistol grip, forend and butt while the metal components were inlaid in the typical fashion. The bolt handle was turned down over the right side of the body and iron sights were present along the top of the receiver (tangent type) and just aft of the muzzle in the usual way. Sling loops allowed for a shoulder strap to be utilized for marches and transport (these slings were located under the butt and along the forend). A short piece of wood was added over the forend to act as a handguard over the base of the barrel - the handguard affixed between the rear sight and the first barrel band. The remainder of the barrel was only slightly exposed ahead. The curved assembly sat within a trigger ring that was connected to the magazine ahead. The weapon was loaded by way of "charger" or "stripper clips" through a port along the top of the receiver - guided in and forced down by the thumb until clicked into place. The bolt-lever was then actuated in the traditional way to introduce a fresh cartridge into the chamber (the cartridge being "stripped" off of its clip) while ejecting any spent shell casing within. Solid and reliable, the Italian Modello 1891 was a fine addition to the bolt-action ranks of the time. The weapon was chambered for six rounds of 6.5x52mm Mannlicher-Carcano rimless cartridges - the cartridge having been specially designed for the new Italian service rifle. Like other service rifles around the globe, the Modello 1891 held the ability to mount a field bayonet under the muzzle for close-quarters work at a time when bayonet combat in-the-field was still an accepted part of warfare.
As was common practice of the period, the Modello 91 was quickly developed into a cavalry carbine form - essentially a shortened, handier version of the full-length service rifle. Despite carrying the "Moschetto da Cavalleria Modello 1891" (Model of 1891), the carbine was actually adopted some time later in 1893. Its arrangement was consistent with other carbines of the age featuring a half-stock (lacking the handguard) assembly and shortened barrel while largely retaining the function of the original. Additionally, the bayonet mounting (a sliding catch type) was on a swivel which allowed it to be folded back under the barrel when not in use. The result was a more compact, lighter offering suitable for mounted infantry. In 1903, the cavalry carbine was further revised by introducing a "push-button" bayonet release and a short piece of wood added to act as the handguard over the barrel.
The "Moschetto per Truppe Speciali Modello 1891" (M1891TS) variant was based on the cavalry carbine though completed with a full stock and a different nose cap along the forend for supporting the detachable bayonet system introduced on the cavalry carbine. With its full stock, the M1891TS was slightly heavier than the cavalry carbine but still lighter than the original Model 1891 rifle.
Following suit with other militaries after World War 1, the Italian Army decided to shorten their stock of Modello 1891 guns in 1924. This was done to relieving the need of having to field both a long gun and carbine concurrently, thusly simplifying logistics and providing infantry with a more manageable long gun in-the-field. The initiative produced the "Modello 1891/24" designation that came complete with a 17.7-inch long barrel. While similar to the aforementioned carbine developments, the Modello 1891/24 was given a rifle-style rear sighting device which was an improvement over the previous type. The Modello 1891/24 was then adopted as the standard Italian Army infantry service rifle in the lead-up to World War 2. A specialized cavalry carbine version was also issued to special troops as the "Moschetto Modello 91 Per Cavalleria" and these featured a folding bayonet function.