Hammer retarder


The hammer retarder is a component of the automatic firearm that delays the hammer fall and thus reduces the rate of the fully automatic fire.
The retardation of the fall serves two purposes:
  • delaying the shot until the bolt is fully locked;
  • decreasing the speed of firing to improve the firing precision.

    Early 20th century

French designers were among the first to implement adjustable rate-reducing systems. The 1905 Puteaux machine gun featured a mechanism that allowed the operator to vary the cyclic rate of fire between 8 and 650 rounds per minute. This concept was further refined in the St. Étienne Mle 1907, which utilized a complex hydraulic rate reducer. Unlike the mechanical inertia-based hammer retarders of later assault rifles, the St. Étienne's system used a hydraulic piston to delay the action, allowing for a variable rate of fire from as low as 8 rounds per minute up to 600 rounds per minute. The weapon's rate of fire was also controlled by an adjustable gas regulator featuring gas ports of varying diameters. This mechanism allowed the operator to alter the cyclic rate by changing the volume of propellant gas admitted into the gas expansion chamber. In practice, the smaller gas ports were prone to fouling with carbon deposits during sustained fire, and crews were generally forced to rely on the largest aperture setting.

AKM

Use of a cyclic rate reducer is the main difference in the operation of AKM when compared to AK-47. The hammer retarder of AKM is located alongside the trigger and the semiautomatic sear and replaces one of the twin lugs on the trigger. The cyclic rate reducer functions by momentarily holding the hammer in the cocked position after the automatic sear has disengaged. The hammer has to overcome the inertia of the heavy rate reducer before it is released; this causes a slight delay, with a resultant decrease in the automatic rate of fire.

Examples

  • FN BAR
  • FB PM-63
  • Bushman/Parker-Hale PDW
  • Star Si 35