Clean , warm mould .
Generally if the bands fail to fill out uniformly it's a dirt issue , usually oil or some protecterant .
If it is unique to the base or parting quadrant it may be a venting issue . Clean the faces and check the cavity for edge burrs that may be obstructing vent lines .
If you have wrinkles/lines/drips on the bullet the usual suspect is a mould not hot enough .

As a last basic test add tin . Like soap added to water it makes the tin "wetter" and breaks surface tension allowing better flow .

Much of this to follow assumes a new iron Lyman mould for terminology , you named a 454242 I'm not familiar with but I know the 454424 well with a copy in both Lyman and NOE .

Advanced issues if all else fails .
The sprue pour hole may be too small for the mould . We're talking about .01s too small here not bust out the fraction drills and open'er up to 1/4" , it's more like a 40-45° chamfer tool and break a line .002-3 wide in the bluing and square off the inside of any raised burrs.

Break the top edge of the mould facing the sprue plate . Do this as a last resort , again we're talking about being able to see the break edge in the bluing .

Aluminum moulds generally don't need to have the top break done but even the best quality examples can have a burr or some other something in a vent line it's been known to be dust .