Krell Anti-Materiel Rifle
The Warrors of Krell have recovered large amounts of MP ammunition. What they lack is the weaponry. The 20mm AMR is one of their solutions [note: this idea first appeared in an old Space Gamer magazine]
Caliber: 20mm (fires all MP 20mm autocannon ammo)
Operation: manual operated, bolt action
Barrel: 920 mm
Weight: 19.2 kg with scope and bipod
Length: 1330 mm
Feed Mechanism: single shot, manual loading
Maximum effective range: about 1800 meters
The 20mm round fires the 130 gram (2000 grains) projectile at muzzle velocities about 850 meters per second. This results in high terminal effectiveness but also imposes a serious problem of excessive recoil forces. The 20mm round generates about 4 times more recoil when fired from 20 kg rifle, compared to .50BMG (12.7x99mm) round, fired from 10kg rifle (such as Barrett M95).
To make the recoil more or less bearable by the average shooter, the Krell designers developed a quite interesting counter-recoil system, that uses a reactive principle. The system consist of the large reactive tube, located above the barrel. The forward end of this tube is connected to the barrel at about its middle point. The rear part of the tube forms the reactive nozzle. When gun is fired, some hot powder gases are fed from the barrel to the reactive tube and back, forming a back-blast with reactive force that cats again the recoil forces. The large muzzle brake further helps to decrease the recoil. This reactive system, once popular in large caliber (about 80 – 100 mm and bigger) recoilless rifles, almost never had been used in such relatively small weapons. This system, while effective in counter-recoil, has some disadvantages, First, it requires some special firing techniques for shooter to avoid damage from backblast. Second, due to the backblast, it is dangerous when fired inside buildings or too close to walls. Third, the backblast is HIGHLY noticeable and can easily give away the position of the rifle.
The rest of the system is relatively simple. The rotating bolt locks the barrel by three massive lugs. The AMR is a single-shot rifle (no magazine). The shoulder rest and the pistol handle with trigger are located under the barrel – a bullpup design. The weapon has no open sights, instead it has an optical sight (usually scavenged from a hunting rifle) which is mounted on the barrel and offset to the left.
note: this weapon is inspired by the Croatian RT-20