Caliber: 4.5×26 mm Rimfire (special ammunition)
Action: gas operated
Overall length: 840 mm
Barrel length: 640 mm
Weight: 2.7 kg less magazine
Rate of fire: 1,800 rounds per minute
Magazine capacity: 50 rounds
The Interdynamics MKR assault rifle was another unsuccessful and unconventional design of the Swedish company Interdynamic AB. Interdynamic MKR assault rifle appeared during 1980s on the top of the "micro-caliber" craze. The idea behind micro-caliber (less than 5 millimeters / .20 inch) ammunition was to achieve high velocity, flat trajectory and good penetration in automatic weapon, and with low recoil. The Interdynamics cartridge was based on .22 Winchester Magnum Rimfire cartridge case, with curved taper and 4.5mm / .177" caliber pointed bullet, made of solid brass. Lightweight bullet (1.58 g / ~24.4 grain) achieved a muzzle velocity of about 1000 m/s (3270 fps). The effectiveness of this bullet was claimed to be on par with 5.56x45mm bullet at the ranges up to 300 meters. Unsurprisingly, the stopping power of such tiny bullet was questionable at its best, and use of rimmed, rimfire ammunition obviously compromised the reliability of the rifle. As a result, Interdynamic MKR assault rifle remained only in prototype stage.
Because of the combination of thin-walled rimfire case and high-pressure powder charge, MKR rifle was designed to use locked breech, gas operated action with vertically tilting bolt. Rifle fired from the open bolt position, in single shots, 3-round bursts abd full automatic mode. Due to intentionally high rate of fire (~30 rounds per second) the 3-round burst seems to be a preferred mode of fire from this weapon. Rimmed ammunition was fed from double stack semi-circular magazines, located behind the pistol grip, so the overall layout can be classified as bullpup. Magazines were designed as one-use plastic units, loaded at factory and discarded after use. Spent cartridges were ejected downward through the chute that runs inside the stock, just behind the magazine housing. Ambidextrous charging handle was located at the top of the plastic receiver. Carbine version of the MKR rifle was similar in design, but had shorter barrel.