Are you seating the bullet all the way to the front edge of the front band. I make a dummy round and play with it till I get it right, when it will fit the barrel I move on. Sometimes they don’t plunk but require a little pressure from 1 finger to give it that last 20-30 thou into the chamber. This is usually brass being a hair short and not getting the firm taper crimp I normally give them. I start with OAL and then build the load form that.
Load 10-15 and test for function under pressure. I haven’t had any issues yet but have only shot 2 cast bullets through mine. An RCBS 45-200, which is identical to the Lachmiller that Rick posted in post 2 and a 452-230 TC Lee. All sized.452. My Kimber custom 2 will feed them and it’s still brand new and very tight.
This is what has worked for me, I’m sure there are bullets out there that just won’t feed no matter what you do.