I have a Mossberg 590A1 with a Vang Comp barrel that I use for HD.
From the VCS website (
www.vangcomp.com)
"The alterations to the barrel consist of lengthening the forcing cone, back-boring the barrel, and adding compensating ports. With the VCS, accuracy significantly improves, felt recoil is dramatically reduced, and muzzle rise diminishes. By lengthening the forcing cone, the pellets have a smooth flow from the chamber to the bore. This prevents the pellets from bunching up in the barrel and reduces the felt recoil. In addition, the pellets do not become as deformed and keep a more consistent shape.
With less deformation and a less turbulent flow, the pellets achieve a higher rate of accuracy. Back-boring the barrel is accomplished by boring the barrel from the chamber towards the muzzle creating a choke where there was none. Back-boring is a key portion of the VCS modification and aids in both increasing accuracy and reducing felt recoil.
Probably one of the most important and most obvious parts of the VCS are the compensating ports. Some of the gases, created by the burnt powder exiting the muzzle, vent upward through the ports. This redirected gas flow helps prevent the muzzle from rising and allows for both increased accuracy and a more rapid recovery time between shots. Also, the ports reduce muzzle flash, which in turn helps to retain night vision and keep the shooters location less conspicuous in low light conditions.
In combination, the lengthened forcing cone, the back-boring, and the compensating ports make up the Vang Comp System. The VCS has been estimated to reduce felt recoil by about 15%. The increase in accuracy is dramatic. For example, patterns using 9 pellet 00 buck are as tight as 2 3/4" at 15 yards and 10 to 12" at 25 yards. Also of note, all modifications, except the compensating ports, are internal.
No extra parts are added to the barrel. Thus, the VCS barrel requires no maintenance other than normal cleaning. Also, other types of specialty ammunition, such as slugs, can be used in the Vang Comp System. The VCS, developed to maximize performance of the tactical shotgun for Law Enforcement and Military applications, is covered by three U.S. Patents. Currently only Mr. Vang's California facility produces the VCS. "
I cannot tell you how impressed I am with this system, the patterns are very tight but more importantly very consistent. I am not a very recoil sensitive person but the recoil reduction caused by adding the ports to the muzzle allows for very fast follow up shots not to mention that they reduce muzzle flash in low light. The system is a huge improvement over cyl. or imp. cyl chokes but I recommend patterning any shotgun/ammo combination so that you are very familiar with the limits of your weapon system and load, for example, with estate tactical low recoil 00 buck or federal tactical 00 buck, my maximum range is 30-35 yards with all 9 pellets contained in the thorasic cavity of an average sized human body. BarSto and Vang Comp have recently partnered up to produce barrels with the VCS system for several different shotguns... I will be ordering a BarSto barrel for my Benelli M1 Super90 as soon as they are available.
Hope this helps,
Trevor