The Chassepot, officially known as Fusil modèle 1866, was a bolt action military breechloading rifle, famous as the arm of the French forces in the Franco-Prussian War of 1870 and 1871. It replaced the obsolete muzzle-loading Minié rifle. It was a great improvement on the military rifles previously in use and marked the real commencement of the epoch of bolt action, breech loading, military firearms generally. It was easily converted to fire metallic cartridges in 1874 (Gras rifle), a step which would have been impossible to achieve with the Dreyse needle rifle.
It was manufactured by MAS (an abbreviation of Manufacture d'Armes de St. Etienne, Manufacture d'Armes de Chatellerault (MAC) and Manufacture d'Armes de Tulle (MAT). Many were also manufactured under contract in England (Birmingham), Belgium (Liege), Placentia and Brescia(Italy). The approximate number of Chassepot rifles available to the French Army in 1870 was close to 1,200,000 units. Manufacturing of the Chassepot rifle ended in February 1875, four years after the end of the Franco Prussian War.
In the Franco-Prussian War (1870-1871) it proved greatly superior to the German Dreyse needle gun, outranging it by 2 to 1. Although it was a smaller caliber (11 mm vs. 15.4 for the Dreyse), the chassepot ammunition had more gunpowder and thus faster muzzle velocity (by 33% over the Dreyse), resulting in a flatter trajectory and a longer range which was 1200 yards (1100 m). The Chassepots were responsible for most of the Prussian and other German casualties during the conflict.
The breech was closed by a bolt similar to those of more modern rifles to follow. Amongst the technical features of interest was the method of obturation of the bolt with a shielded rubber ring which was quite effective. It was similar in principle to the de Bange obturator for artillery. The Chassepot used a combustible paper cartridge holding an 11mm (.43 inch) round-headed cylindrical lead bullet. An inverted standard percussion cap was at the rear of the paper cartridge and hidden inside. It was fired by the Chassepot's needle (a sharply pointed firing pin) upon pressing the trigger. While the Chassepot's ballistic performance and firing rates were excellent for the time, burnt paper residues as well as black powder fouling did accumulate in the chamber and bolt mechanism after continuous firing. Also, the bolt's shielded rubber ring did erode in action but was easy to replace in the field by infantrymen. The older Dreyse needle gun and cartridge had been deliberately constructed in a way to minimize those problems but to the detriment of its ballistic properties.
In order to correct this problem the Chassepot was replaced in 1874 by the Gras rifle which used a center fire drawn brass metallic cartridge . Otherwise, the Gras rifle was basically identical in outward appearance to the Chassepot rifle. Virtually all rifles of the older Chassepot model (Mle 1866) remaining in store were eventually converted to take the 11mm Gras metallic cartridge ammunition (fusil Modèle 1866/74).