For a purely decorative rifle, one would be hard pressed to find a class more fanciful than the old schuetzen class rifles, as have been used in Europe for centuries.
..But they are not just closet queens..they can shoot! Schuetzen competition is very old..perhaps somebody here, can rustle up a date when it really started. I found 1842, but not earlier...
It began with the Germanic speaking peoples of Europe, likely Germany or Switzerland. Since the competitor only takes his rifle
out to shoot once or twice a year, it looks like part of the competition, is tom have the most "ahhhs" producing rifle in town.
The sport spread to the UK, and then to the USA, at Creedmore, Long Island, NY...where competitors seemed to be not so taken with carvings and engravings, the rifles becoming more utilitarian in appearance.
https://www.recoilweb.com/story-of-the-schuetzen-rifle-145154.html