6.5×52mm Mannlicher-Carcano

6.5×52mm Carcano or 6.5×52mm Paraviccini-Carcano is an Italian military 6.5 mm (.268 cal, actually 0.2675 inches) rimless bottle-necked rifle cartridge, developed from 1889 to 1891 and used in the Carcano 1891 rifle and many of its successors. A common synonym in American gun literature is "6.5mm Italian". In American parlance, "Carcano" is frequently added to better distinguish it from the rimmed hunting cartridge 6.5×52mmR (U.S. version: .25-35 Winchester). Ballistically, its performance is very similar to that of the 6.5×54mm Mannlicher-Schönauer.

Design
Under the direction of the "Commissione delle Armi Portatili" (Commission for Portable Weapons), instituted in 1888 to develop a smokeless-powder rifle for the Italian Army, the "Reale Laboratorio Pirotecnico di Bologna" (Royal Pyrotechnical Laboratory of Bologna) developed and tried several different cartridge designs, with a bullet diameter from 8 mm to 6 mm. Finally, due also to the influence of Major Antonio Benedetti, of the Brescia Arsenal, Secretary of the Commission and strong supporter of the advantages of smallbore cartridges, the 6.5×52 cartridge was adopted in March 1890, prior to the adoption of the rifle that used it (the Model 1891 Carcano rifle).

After the adoption of the cartridge, the arsenals technicians worried about the characteristics of the original ballistite load, since that propellant was considered too erosive (flame temperature of 3000-3500 °C) and not stable under severe climatic conditions. Several other loads were tested, including the British cordite but without good results, until the Reale Polverificio del Liri (Royal Explosives Factory of Liri) developed a new propellant called "Solenite", composed of trinitrocellulose (40%), dinitrocellulose (21%), nitroglycerine (36%), mineral oil (3%), and shaped in large tube-like grains. The new propellant, that reduced the flame temperature to 2600 °C and proved to be very stable, was adopted in 1896 and never changed until the end of the military production of the cartridge.

The 6.5×52mm Carcano was designed as a full-blown infantry cartridge. In accordance with the tactics of the time, the adjustable rear sight of the rifle allowing for volley fire up to 2,000 metres. The 6.5×52mm Carcano was the first to be officially adopted of a class of similar smallbore military rifle cartridges which included the 6.5×50mm Arisaka (Japan), 6.5×53R Mannlicher (Romania / Netherlands), 6.5×54mm Mannlicher-Schönauer (Greece), 6.5×55mm Swedish Mauser (also Norwegian Krag-Jørgensen), 6.5×58 Portuguese.

A comparison with larger bore smokeless powder cartridges of the 7.62mm and 8mm calibre class (which class started in 1886 with the French 8×50mmR Lebel, continuing with the German 7.92×57mm, the Austrian 8×50mmR, the .303 British, the Russian 7.62×54mmR, the Belgian and 7.65×53mm Argentine, the .30-40 Krag, and the much later .30-03 and .30-06 Springfield) may make the 6.5mm rounds appear "underpowered" on paper though, and lacking in stopping power. On the other hand, the small bore cartridges seem to have a long list of advantages, as flatness of trajectory, outstanding penetration at distance, less weight, less recoil, smaller dimensions, and less material required in production.

Its short-lived intended successor cartridge, the 7.35×51mm Carcano, is sometimes identified as the first intermediate cartridge, before the German 7.92×33mm and the Soviet 7.62×39mm.

The original 6.5×52mm barrel design, developed by the Brescia Arsenal at the same time as the cartridge before development of the M91 Carcano Rifle itself, used a gain twist barrel with deep rifling to reduce wear, extend barrel life and give consistent accuracy. Gain twist has a slow initial twist in the barrel progressively getting faster until the final twist rate is attained near the muzzle, resulting in less torque being imparted to the bullet during the highest stress phase of the interior ballistic cycle, and thus less barrel wear in the throat of the barrel. (Gain twist was phased out in the last production of the Carcano rifle in favour of conventional rifling.)

Performance
With properly-bulleted ammunition, the 6.5×52mm Carcano is an effective deer cartridge up to about 200m (220 yards). Its main drawback in military use was that the standard Italian service round used a round-nosed, highly stable bullet that usually didn't tumble unless it hit bone, causing many narrow-channel, straight-through wounds. This characteristic is due to its high "sectional density" (the ratio of a projectile's weight to its diameter).

Hand loaders should note that the currently available factory ammunition may lack accuracy due to use of a 6.7mm (.264 in) bullet instead of the 6.8mm (.268 in) as originally loaded.

Notable uses
The cartridge has achieved some notoriety, as a World War II Italian Carcano rifle was identified by the Warren Commission as the weapon used by former Marine Lee Harvey Oswald in his assassination of President John F. Kennedy.