From the thread on handloading.
this mold is throwing bullets anywhere from .431 to .437
But now you changed this thread to .449-.458. That's a lot closer to where it should be. The .449 bullet is probably not filled out completely, the .458 bullet is caused by NOT having the mold closed all the way tight. You have to have the mold hot, the lead hot, and the mold closed tightly.
I've got 8 different 6 cav lee's ALL of them work well, they are all within 5 ten thousandths of what they should be. That's not saying they can't make a bad one. But your inconsistency shows OPERATOR ERRORS. If all your bullets were round, and all the same diameter but undersized, or over sized, then the mold is at fault.
Take a long look at the mold. Does it close tight? Hold the closed mold up to a bright light, try to see if you can see light coming through between the closed halves. If you can, then there's something holding them apart. The guide pins have to go all the way into their sockets, and there CANNOT be any lead on the blocks that will hold them from closing.
If there's some lead stuck to the block faces, be very careful getting it off. Use a sharp wooden stick, nothing harder. The soft aluminum is easily damaged.