The latest Z Series competition shotgun from Zoli is the Z Trap Unsingle shotgun. It features a rib that can be adjusted precisely with a micrometer, either vertically (parallel with the bore), or at an angle to change the point of impact.
From the press release …
Antonio Zoli, makers of the Z Series competition guns for Sporting Clays and Skeet, announced the introduction of the long-anticipated Z Trap Unsingle shotgun. Based on the highly successful Z Series action with removable trigger mechanism, the Z Trap Unsingle has an innovative adjustable rib and comb system which allows the shooter to adjust the rib and comb height parallel to the bore as well as change the point of impact. The adjustment of POI with the rib is done via simple micrometer wheels which allow the shooter to raise the pattern over 150%.
The Z Series starts at $5999, I am not sure the Unsingle is available at this price.