They were a rather strange design (especially the carriages) that came in 6 and 12# sizes. It's strong point is that it could be elevated much higher than a conventional gun. Union used. Both sizes illustrated Photo LoC
Here's another Wiard of apparently larger caliber standing by itself along the Stones River park tour route we saw while on our way to the Visitor Center. One big drawback to the success of these guns was the death of their inventor, Norman Wiard, in the premature discharge and I think explosion of one of his guns during testing.
Shiloh National Military Park currently has eight of the 6-pounder Wiard rifles, and six of the 12-pounders. All of them have been, or are scheduled to be, given replica Wiard carriages.