Not directly related but the pictures of obturators reminded me of this accident report:
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/727954/20180823-Challenger_SI_Castlemartin_Redacted_RT.pdf
In short a sad story of firing the main gun without the obturator fitted excerbated by poor storage discipline.
Apart from the safety lessons there are interesting details of a modern breech system.
Robert G8RPI