The Payload Bulkhead interfaces between the Avionics Bay and the Nose Cone, and more specifically between the piston, the Avionics tower, and the Payload. All load from main parachute opening will go through the Payload bulkhead (whereas we expect all reaction load from piston separation to go through the Avionics bulkhead)
Rev. 1: Pathfinder
The Pathfinder revision was a basic flat plate with a centering ring welded on.