Vent rib barrels.

[LynnMassGuy]

What are they for? Are you supposed to sight down the flat part of the rib?

 

[Dave McCracken]

No. The big reason for the rib is to eliminate heat mirage. One often hears that the rib helps to "Lead" the eye to the target, but most of us just see the rearmost part. If you can see all the rib, your shotgun is probably shooting rather high.

Ribs, both ventilated and solid, have little utility on a hunting gun. It's seldom one gets fired fast enough to build up enough heat for distortion. They look spiffy and the maker can charge more for a shotgun with one, explaining their popularity.

 

[9mmMike]

I like the VR barrels because they raise the front bead/sight. I only have one plain barrel here at casa del 9mm and it happens to be on the gun that I am using for clay games. I am planning on changing it to a VR barrel simply because I am hurting my cheek by cramming my face down on the stock to align my eye.
Prior to the plain barrel, I shot mostly tall, rifle-sighted barrels and never got hurt at all. A VR is a good compromise for me and it allows a higher cheek-weld.
Since I shoot in all weather, I am not too keen on VR's for post-shoot cleaning. It adds a ton-o-time to the cleanup if you shoot in the rain and snow like I do.
Obviously YMMV.
Mike

 

[Chris Rhines]

They provide an excellent place to cut dovetails for a set of rifle sights, if that's your thing.

- Chris