I've seen a few postings about the Vang Comp System and wanted to add some information. Keep in mind this type of modification is not recommended by Benelli and probably voids your factory warranty.
The Vang Comp System designed by Hans J. Vang, is a set of modifications to your shotgun barrel consisting of lengthening the forcing cone, back-boring the barrel, and adding compensating ports. Mr. Vang has paired with DVC Armaments / GG&G to produce barrels that allow these modifications to be completed on the Benelli M1 Super 90 based shotguns. While I haven't been able to acquire much information about the process it appears to work like this. You are required to send in your barrel and it's cut apart to build the new barrel. The reason for the new barrel is stock Benelli barrels are too thin and overbored.
Well I'm here to make Benelli lovers aware this can and has been done quite extensively by several shotgun specialist without building a custom barrel. Three very reputable names in the shotgun industry do these same modifications to your original barrel. Ballistic Specialties, Briley Manufacturing, and Seminole Gunworks all have experience performing these modifications to the Benelli.
Depending on which company does the work your barrel can be modified to the following specifications.
Forcing cones lengthened to 3" or 5"
Backbore to .733" or .735" diameter
Choked to spec or interchange style choke tubes
Porting
Other accuracy modifications can be done such as trigger jobs and component polishing.
