The Lott Chamber as Jack Lott designed it, has no step at the end of the neck area. He said he designed it with a sloping entry into the throat to prevent guilding metal shaving if shorter ammunition, specifically .458 Win Mag was fired from it - that was the BIG change and sole reason for it's existence.

The .450 Watts was already 'out'.

All other chambers have a 90 degree 'step' at their end. 1/2 way up the 90 degree angle, is a 45 degree slope into the leade or freebore, whichever it has. BR shooters call that 45 degree slope, "That Mean Little Shoulder".