Trapdoor mechanism

In firearms, a trapdoor is a form of breech-loading mechanism for rifles, where a hinged breechblock rotated up and forward, resembling the movement of a trapdoor. The Springfield models 1865 and 1873 were best known for first employing this type of action.

The trapdoor mechanism employed a hinged breechblock 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 breechblock caused these rifles to be named "Trapdoor Springfields".

The conversion from musket to breechloader was done by milling open the barrel's breech section and inserting a hinged trapdoor 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 The rack-type system extractor was withdrawn automatically as the breechblock was opened and snapped back at the end of its stroke.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.

Approximately 5,000 Civil War Model 1861 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, to be called the "Second Allin".

The Springfield model 1865 fired a rimfire .58-60-500 cartridge (.58 inch 500-grain (32 g) bullet, 60 grains (3.9 g) of black powder), the caliber matching that of the Civil War Minié ball, 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.

In 1872–1873 a military board, headed by Brigadier-General Alfred H. Terry, conducted an examination and trial of 99 rifles from several domestic and foreign manufacturers including those from Springfield, Sharps, Peabody, Whitney, Spencer, Remington, and Winchester pursuant to the selection of a breech-loading system for rifles and carbines for the U.S. Military.

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