The KRISS Vector series are a family of weapons based upon the parent submachine gun design developed by the American company KRISS-USA, formerly Transformational Defense Industries (TDI). They use an unconventional delayed blowback system combined with in-line design to reduce perceived recoil and muzzle climb.
The Vector uses an articulated mechanism referred to as the “KRISS Super V,” which allows the bolt and an inertia block to move downward into a recess behind the magazine well. The theory is that at the end of this travel, the energy is transmitted downward rather than rearward, thus reducing the felt recoil. When fired, the barrel axis is in line with the shoulder as in the M16 rifle, but also in line with the shooter’s hand. This is intended to reduce muzzle climb when combined with the off-axis bolt travel, though it also greatly raises the sight line in comparison to the bore axis. The initial prototype model by TDI achieved a rate of fire of 1,500 rounds per minute (RPM), though this was brought down to around 1,200 rounds per minute (RPM) on the production models.
The Vector is split into two major assemblies in a similar manner to the AR-15 rifle, secured together with four push pins. Due to the weapon’s unusual layout, the lower contains the action, charging handle, magazine well and barrel, while the upper contains the ejection port, rail system, pistol grip and fire control components, as well as the stock for configurations that have one. This modular design allows for toolless caliber conversions by swapping out only the lower. The Vector’s safety is ambidextrous (as well as the fire mode selector on the auto trigger pack) while the ejection port, charging handle, bolt release catch and magazine release are not, and are only available in a right-handed configuration.