I fired a few shells a little while back and I found that my lift was a little bit lacking for my 4 inch shells but seemed fine for 3 inch shells. I used proportionately more for the 4 inch so I'm not 100% sure I understand the problem. My BP is not brilliant and I use a bit more than 10% to compensate, it's granulated through a grater and as I aid lifts 3 inchers fine. The 3 inchers do seem seem to be a better fit.
What's more I actually had a little commercial BP for one shell and the lift was adequate but not totally satisfactory. I'm using cardboard tubes for now and even after 8 layers of pasting there is a sizeable gap around the shell. I suspect this does not help and I wondered if anyone has packed out a shell in some way...e.g. a thicker cardboard layer to start just to get the fit better. I've seen some cylinder shells being loaded that literally have to be forced down the tube and I know how pressure plays a huge role in the way BP burns.
Would adding a layer of thicker board as a base layer ruin my breaks?