The points that you have asked about, the cam loaded barrel nut locking plunger v the mag cover plus the ramp to tighten up the extractor have all bee explained in articles regarding the Bren on this very forum.
The ramp tightens up the extractor and positively locks it to the spent/fired case to ensure that the extractor cannot loose its grip immediately after firing and during the violent primary extraction and unlocking. There's nothing gentle here......... The ejection is a pretty violent cycle too. That's why the ejector stakes the rim of the primer, to prevent 'caps-out' which plagued the original ZB .303" trials guns.
During our long years as apprentices, in the classroom, we would try to simulate the violent unlock, extract and eject cycle using strong cable tied to the cocking handle. Alas, we'd never replicate the real thing. Not even 'Big John' Hessle, at 16 years old, 6'4" and built like a brick out-house could replicate it.
The operating cycle...... FIRE, unlock, extract, eject, cock, feed. load, lock - FIRE