The Springfield Model 1865 was an early breech-loading modification of the Springfield rifle musket design.

During the U.S. Civil War, the advantage of breech loading rifles became obvious. The rifled musket

Rifled musket

The term rifled musket or rifle musket refers to a specific type of weapon made in the mid-19th century. Originally the term referred only to muskets that had been produced as a smoothbore weapon and later had their barrels rifled...

s used during the war had a rate of fire of 3 or 4 rounds per minute. Breech loading rifles increased the rate of fire to 8 to 10 rounds per minute with the additional advantage that they can be loaded from a prone rather than standing position, reducing the visible cross section of the rifleman and thus vulnerability to counter-fire. As the Civil War drew to a close, the U.S. Ordnance Department requested prototypes of breech loading weapons from arms manufacturers all over the world.

After considerable testing, the prototype developed by Erskine S. Allin of the government-operated Springfield Armory

Springfield Armory

The Springfield Armory, located in the City of Springfield, Massachusetts - from 1777 until its closing in 1968 - was the primary center for the manufacture of U.S. military firearms. After its controversial closing during the Vietnam War, the Springfield Armory was declared Western Massachusetts'...

 was chosen for its simplicity, and the fact that it could be produced by the modification of existing Springfield Model 1863

Springfield Model 1863

The Springfield Model 1863 rifled musket is a .58 caliber rifled musket produced by the Springfield Armory between 1863 and 1865.The Model 1863 was only a minor improvement over the Springfield Model 1861. As such, it is sometimes classified as just a variant of the Model 1861. The Model 1861, with...

 muskets. These modifications cost about $5 per rifle, which was a significant savings at a time when new rifles cost about $20 each. Patent No. 49,959 was issued to Erskine S. Allin on September 19, 1865, describing the design.

The conversion from musket to breechloader was done by milling open the breech section of the barrel and inserting a hinged bolt fastened to the top of the barrel. A thumb-operated cam latch at the rear of the breechblock held it shut when in closed position. The rack-type system extractor was withdrawn automatically as the breechblock was opened and snapped back at the end of its stroke. The firing pin was housed within the breechblock. The hammer nose was flattened to accommodate the firing pin.

The breech mechanism employed a hinged breechblock

Breechblock

A breechblock is the part of the firearm action that closes the breech of a weapon at the moment of firing....

 that rotated up and forward, resembling the movement of a trapdoor, to open the breech of the rifle and permit insertion of a cartridge. The hinged breech block caused these rifles to be named "Trapdoor Springfields".

Approximately five thousand civil war Model 1861

Springfield Model 1861

The Springfield Model 1861 was a Minié-type rifled musket shoulder arm used by the United States Army and Marine Corps during the American Civil War. Commonly referred to as the "Springfield" , it was the most widely used U.S...

 rifled muskets were converted at the Springfield Armory in 1866. It soon became apparent that many of the small working parts in the breech system were not going to have a long service life, and the action was too complicated for normal service use. Therefore, before the Model 1865 production order was completed, a less complex rifle was already being tested. This caused the Model 1865 to be called the "First Allin", and the following revised model, the Springfield Model 1866

Springfield Model 1866

The Springfield Model 1866 was the second iteration of the Allin-designed trapdoor breech-loading mechanism. Originally developed as a means of converting rifled muskets to breechloaders, the Allin modification ultimately became the basis for the definitive Model 1873, the first breech-loading...

, to be called the "Second Allin".

The Springfield model 1865 fired a rimfire .58-60-500 cartridge (.58 inch 500 gr bullet, 60 gr of black powder), the caliber matching that of the civil war minie ball

Minié ball

The Minié ball is a type of muzzle-loading spin-stabilising rifle bullet named after its co-developer, Claude-Étienne Minié, inventor of the Minié rifle...

, which was originally used in these rifles.

The Model 1865 quickly became obsolete, and most of them were sold in the 1870s to several American arms dealers. At the time, there was a large demand in the US, for shorter cadet style rifles. To satisfy this need, these dealers cut the barrels and stocks to make short rifles with 33" and 36" barrel lengths. Likewise, the stock wrists were often thinned for cadet use.