Bullpup

Bullpup refers to a rifle configuration that increases the barrel length relative to the overall weapon length. Thus it permits shorter weapons. The design was invented at the Royal Small Arms Factory at Enfield in the United Kingdom, where several years of research led to the construction of the EM1 and EM2 assault rifles.

In a normal rifle, the barrel lies at the very front of the gun, with the firearm action (or mechanism) behind that, and finally the stock at the extreme rear. The trigger is located directly under the mechanism, with the magazine placed in front of it.

In the bullpup configuration the magazine is instead located behind the trigger, which allows the entire mechanism to be moved rearward, reducing the length of the weapon some 20%. The trigger mechanism of some bullpup weapons uses a flexible rod or similar system, which has the disadvantage of a heavy and sluggish trigger pull, but the SAR-21 uses a stiff sliding plate.

Bullpup weapons have been the subject of some debate. Mechanisms typically eject casings to the side. This means that the typical bullpup design must be fired from only one side of the body, or the casings will hit the operator in the face. Some weapons have allowed the ejection to be switched by re-assembling it, while others, like the FN F2000 and A-91, eject forward, and others, like the FN P90, eject downward, meaning the magazine must be mounted on the top or sides of the weapon.