I have had several Numrich rifles, mostly Underhammer, however, I have had two swivel rifles.
The idea is great, but the two that I had, the barrels were way too thin, where the drum was.
And the locks were not very good.
Even the indexing holding the barrels was not the best.
The ballbearing wore a track in the barrel (breech), that eventually the barrel position would not hold.
I do hope this helps
Fred