I would tend to agree with Double D.

Doubles are shot one barrel at a time so magnaporting the inside of both barrels would be quite a task or impossible.

If one were still to try to limit the rise of the barrel with the expeled gases the only measure basically left would be a standard perforated muzzle brake for each barrel. It may work but it would probably affect the load regulation in addition to being horribly ugly.

Other than having more weight are there other measures to perform on the barrels to decrease recoil rise and increase accuraccy and the speed of follow up shots?