LP, I had NO END of chambering issues with my ca. 2015 Uberti revolver, and chased my tail for a while thinking it was a tight chamber neck issue until I got the idea to use a sticky round to find what seemed to be the tightest chamber, then coat the round in black marker or dyekem- then insert and twist in the chamber, then remove and observe the tight spots. What I found was, while my chamber necks were tight, they weren’t near as tight as I thought. The first issue I found was I was getting little bulges below the crimp (done with the LFCD), even though I was careful not to let the case mouth bump the top edge of the crimp groove. My eventual solution was to get a Redding Profile Crimp Die, and those issues went away. This die is fantastic, but only works well with bullets that have a nose shape similar to the original Winchester bullets, not an issue for me as I use the Accurate 43-215C mold. I also discovered that the sizing die was not pushing the shoulder of the bottleneck far enough down, in fact it wasn’t moving it. I ground a little off the base of the die, but later when I bought my second .44-40 gun (a 2019 Uberti 1873 Rifle) which had the shoulder of the bottleneck further forward in the chamber that I had to take more off the base of the Lee sizing die so the shoulder would be set further back when resizing. I’m not the only one who has had this issue with the Lee .44-40 sizing die. Wish I had not been cheap and bought the RCBS Cowboy dies out of the gate.
In summary, your gun may be sensitive to bullet diameter- but make sure your sizing die is good, and that your crimp doesn’t have bulges either.