Bullpups are firearm configurations in which the action is located behind the trigger group and alongside the shooter's face, so there is no additional space for the buttstock as in conventional designs. This permits a shorter firearm length for the same barrel length for improved maneuverability, and reduces weight.
Origins of the term 'bullpup' for this configuration are unclear. The word is reported as being used in the US in 1957 to denote a target pistol, particularly one with a fancy stock.
The bullpup design places the gun's action and magazine behind the trigger, in front of a short buttstock. This decreases the firearm's length and weight while retaining the same barrel length. Bullpups generally allow for a 25% reduction in weapon length, which allows for better maneuverability in confined spaces.
An often cited shortcoming of bullpups is that, by design, their ejection ports are close to the face, generally making it difficult for left-handed shooters to use due to the fact that firearms in general have their ejection port on the right-hand side and eject spent cartridge casings towards the right. This means left-handed shooters must shoot off-hand, as ejected casings would otherwise hit them in the face. Certain designs, such as the FAMAS assault rifle and the Steyr AUG, overcome this limitation by allowing the bolt and ejection port cover to be swapped, turning the weapon into a dedicated left-handed version. Other bullpups such as the FN P90 and the Kel-Tec RFB solve the problem by designing the ejection port to eject spent casings downward or forward. The FN F2000 utilizes a patented design where spent casings are ejected forward of the rifle.
Additionally, the bullpups extra weight in the rear, may affect balance with respect to muzzle rise, and automatic firing accuracy. However, being held closer to the body, the bullpup design has the advantage of causing less fatigue to the user's positioning arm, when the arm is outstretched for long periods of time. There may thus be a infinitismal reaction time advantage, in raising a bullpup to fire, from a downward pointed direction, will result from a lighter weapon. The bolt may also have to be smaller to be able to fit in the stock, with reduced components, results in reduced overall weight. Being more compact and having a shorter length allows for greater close-in weapons usage, however being of a shorter length, bayonet length effectiveness would be dimensionally reduced. Accuracy at longer distances is oft-cited as a criticism of bullpups, however, if barrel length is of similar dimensions, and all other factors equal, accuracy would be similar. Lastly, due to the forward assembly and the necessary trigger linkage, bullpup trigger pull characteristics are often criticized.
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