Editing Breechblock (section)

===Rotating drum{{anchor|Rotating drum}}===

A rotating drum breechblock or rotary breech consists of a cylinder which rotates on an axis offset from the barrel.  It is also known as a cannon breech because of association with some cannon designs. A [[Geometric terms of location|longitudinal]] cut-out section or eccentric hole provides access to the breech. Rotating the cylinder then closes the breech. The geometry is not unlike the [[Cylinder (firearms)|cylinder]] of a [[revolver]]. In the [[Werndl–Holub rifle|M1867 Werndl–Holub]], the cylindrical breechblock is retained at the rear by the receiver. Mating faces can be profiled (i.e. not faced perpendicular to the axis of rotation) so that the breech tends to seal or fit more closely as it is closed.<ref>[https://www.youtube.com/watch?v=NVqgvyQ0Tvw 1867 Werndl Military Rifle], accessed 14 July 2021.</ref>

the Nordenfelt eccentric screw breech is a variation of this design. Instead of holding the breechblock between the breech at one end and the receiver at the other, in this design the breechblock is threaded around its circumference and is screwed into the breech until it meets the rear of the chamber. The breech is opened by rotating it a fraction of a full turn, until a hole through the breechblock aligns with the bore. The [[Magnum Research]] Lone Eagle pistol is a single-shot pistol chambered for rifle cartridges that also uses a rotating drum breechblock.<ref>[https://www.youtube.com/watch?v=BHQZ6I2BE6E Ordnance Research SSP-91, aka the Lone Eagle], accessed 14 July 2021.</ref>

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File:Colt Autentica.jpg|The geometry of a rotating drum breechblock is similar to the alignment of the cylinder and barrel of a revolver
File:Wanzlbazaar.jpg|The rotating drum breechblock of the [[Werndl–Holub rifle|M1867 Werndl–Holub]] rifle
Werndl rifle Bolt.gif|Animation of the Werndl rifle
File:75mm1897BreechMechanismDiagram.jpg|Drawing showing the Nordenfelt eccentric screw breech mechanism of the [[Canon de 75 modèle 1897|75 mm Field Gun Model 1897 M1]] (US designation)
File:Canon de 75 breech mechanism.jpg|Breech of the Model 1897 in the open position
File:Schertz VFW 04.jpg|Breech of the Model 1897 in the closed position
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