What were they sized to? Sizing a boolit down more than .02 or so in the throat can also give you land marks much closer to the nose than you'd expect. You can check this to a degree by holding a caliper set to bore diameter, (not groove diameter), against an unfired boolit to see how far back from the nose the lands begin contact. If you load a .454 boolit in a .450 bore, you're basically extruding the nose past the start of the lands. My .450 B has groove diameter of .4505 so the bore, (harder to measure accurately), is less than that by the height of the lands.
BD