I had a similar issue when my Uberti 1873 was new. Sometimes it hung up on the loading gate, but it was always hard to replace. The front end needed to be seated first, then the back end could be tapped into place, but it was a very tight fit and the metal started to peen, making the problem worse. I eventually did a bit of filing and stoning, relieving some of the tightness and creating a slight bevel. This resolved the issue.
CC Griff