Sounds like you're not using pure lead. I use .454's in all my .44's.On my 1858 I get a nice ring shaved off on the .451s. And it is quite difficult to shove them down into the bore with the lever. They go down in there hard, not easy. There have been those who have broke off the load lever.
Speers and now Hornady. It says lead on the box, I think. I don't know if it says 'pure'. But if it did, how pure is pure?Sounds like you're not using pure lead. I use .454's in all my .44's.