5.5x45mm Marder Duplex Ammunition
The Marder duplex round is the result of studies undertaken by the Marder Corporation to attempt to increase the hit probability of military small arms. Evaluation of multi-projectile ammunition showed that a two projectile cartridge showed an increased hit probability of 67%, and a three projectile cartridge resulted in a a full 100% increase in hit probability.
The three projectile cartridge proved unsuitable for mass production, so the two bullet or 'duplex' load was chosen for limited production for field trials. The duplex load conatins two nested projectiles weighing 2.68 gram projectiles in place of the typical 4.3 gram M855 projectile. The base of each bullet is beveled to insure dispersion of the two projectiles. The lighter bullets result in less energy, which is deemed by Marder to be acceptable in light of the higher hit probability.
The Marder 5.5mm round incorporates a 'piston primer' that serves to operate Marder's assault carbine and rifle. On firing, the piston primer is projected rearward approximately 2mm. The piston primer acts on the firing pin, propelling it rearward, while cams on the firing pin unlock the bolt from the barrel extension. The bolt is then free to recoil rearward, extracting and ejecting the spent case, and then loading a fresh cartridge into the chamber.
Maximum effective range is specified as 400 meters, slightly less than the M855 5.5x45mm listed effective range of 460 meters. Both Imperial and company studies indicate that 80% of all small arms fire occurs at 75 meters or less, and virtually all occurs at less than 300 meters, thus the performance of the duplex load is considered more than adequate.