I agree with Buffy.
Vang's porting does help in reducing muzzle jump.
I've been working with several shotguns this summer, and in doing a three-gun project a few weeks ago I noticed quite a bit of difference in hotter buck & slug loads between one 870 that was worked over by Vang long ago, and an un-modified 870 PMAX, both with the same 18-inch barrel lengths.
As far as pattern effects go, porting CAN slow down a shot charge or slug fractionally, but most of the bleed-off occurs so close to the muzzle that I'm not sure how much real effect it has, IN ITSELF, on velocities.
The backboring that Vang does probably has more affect on lowering shot charge speeds than the porting alone, but together they do slightly reduce velocities.
The combination of porting, backboring, and forcing cone lengthening all combine to reduce recoil, too.
That project inspired another one, where I fired several different buckshot loads through the PMAX at various distances & measured results, then sent just the barrel to Vang to be worked on.
When it came back, I repeated the earlier baseline protocol.
Patterns were markedly tighter on the second go-round with almost all loads, muzzle rise/cheek slap was also reduced.
The potential for erratic patterning is greatest in the Flitecontrol loads, since their wad is designed to perform to certain parameters that depend on velocity/gas pressure, but even there the second session showed overall tighter patterns with most of the Flitecontrol loads tested.
Working with three Remmies, a Savage, the new Beretta, and a Stoeger coachgun, all in 12-gauge, has shown more pattern variations this year than I've ever encountered before, with some individual buckshot loads actually patterning tighter at progressively farther distances than at closer distances.
Shotgun performance is highly variable, but my experience shows me an overall trend- The Vang Comp barrels produce tighter shot patterns in general than the standard factory barrels I've worked with, and show lower recoil levels.
Denis
