I don't see vierlings very often, but don't recall ever seeing one with three rifle barrels before. Perhaps they are more common (if you can use that term on very limited production items) than I am aware. Just as double rifle drillings seem to be a small percentage of the drilling population, I suspect triple rifle vierlings are similarly low production portion of the vierling population.

This is a very nice piece that would be a great attention getting display item!