I guess it makes sense since barrel cooling is the typical concern with rapid fire. I would expect cooling the barrel would keep the windage manageable--although lead projectiles would probably compensate for that as well. It might be necessary to prevent the barrel from yielding.

I don't know how this action works so I'm guessing. Didn't the Williams binding problem happen at the breech block? If so then I would be concerned about portions of the mechanism of the Hughes expanding while the barrel and breech opening were held cooler, exacerbating a binding problem. On the other hand,the cooling might be helping seal the breech by keeping the breech from expanding too much. Sealing the breech seems to have been a serious problem for ACW breechloading cannon.