Cupped face high power seal with center crowned face to increase the strength of the seal. More meat on the sides to allow sizing if required to fit the varied tubes in these guns. Rear band is already ideally sized and holds lubricant as well as centers the piston in the tube.
These make great power but require great tube tolerances to get power and in bad tubed guns the Vulcan SS seal is better.
In the day of perfect guns these got you the max power possible.
Now bigger with a thicker seal lip for more adjustment- sizing capabilities.