IN SHORT:
Vang Comp Systems was founded in 1990 by Gunsmith and Inventor Hans J. Vang with the mission of bringing innovative, high-quality parts and services to everyone who owns and uses a shotgun. Mr. Vang developed the Vang Comp System at the behest of a government agency which was searching for a way to make their duty shotguns safer to down-range bystanders, i.e. make their scatterguns shoot tighter shot patterns without the use of choke tubes. This government agency also complained about the recoil and night-time muzzle flash of the 12ga shotguns and requested a mitigation of these factors as well….
Mr. Vang devised a system of lengthening the forcing cone of the shotgun barrel to allow a smoother transition of the shot column from chamber to bore, thus decreasing recoil and shot deformation. He would then further back-bore the barrel so that the shot column gradually tapered and squeezed together as it traveled down the bore towards the muzzle. Before they get to the muzzle, the hot expanding gasses which account for the muzzle flash are jettisoned through a precisely-calculated and rigorously-tested array of compensation ports. This hot gas is discarded through 62 holes, 31 on either side of the front sight which contributes to the flat shooting, reduced felt recoil, eliminated muzzle flip and diminished muzzle flash characteristics of the Vang Comp System.
With less deformation and a less turbulent flow, the pellets achieve a higher rate of accuracy. Back-boring the barrel from the chamber towards the muzzle creates a choke where there was none. The rule of thumb allows that a standard cylinder bore barrel will shoot about 1-inch of spread per yard from the target (5 yards from target= 5-inch shot spread).
The Vang Comp barrel modification produces shot patterns that are 2-times tighter.