Lee conical 450-200:
In my opinion they should fit. I use them in Pietta army 1860, cal 44.
I've seen on You-tube - those being fed to Uberti.
Also, I saw Uberti user manual, and they recomend RB and / or conical.
I was thinking to purchase one of the Uberties, so after you try, pls let us know about accuracy of Uberti with conicals. In Pietta, RB works better. (more accurate)