That case has the appearance of a misfed round jamming, not a fired case. The neck of the case has not been blown outwards under pressure but the projectile has been bent upwards and thus came free. Please can you confirm whether the primer was struck, or, better still, show an image of the base and headstamp?
This type of misfeed can occur if there is insufficient magazine spring tension. If mag spring tension is low (it should be wound up by a crank after filling with live rounds) then the round being rammed bounces on ahead of the bolt face in an uncontrolled manner. The extractor of the Oerlikon is a solid machined lip at the bottom of the breech face and the cartridge should slide down the face as it moves into the chamber and engage behind the extractor. If the cartridge rim gets ahead of the extractor then it will jam and cannot be fired. The firing pin/striker of the Oerlikon does not protrude from the breech face until the cartridge is well inside the chamber.
In this case the round seems to have got part way into the chamber before the breech block muscled it aside. The odd shaped hole in the side was caused by the feed face of the breech cutting into it as it was mangled. The "tongue" was left uncut by the groove for the ejector. The brass cut is now folded into the forward part of the case. The denting on the opposite side of the case was caused by the mouth of the chamber.
It is normal practice to leave filled magazines with low spring tension, enough to prevent rounds getting jumbled, to prolong spring life. But they must be "wound up" before shooting. If action is imminent then, of course, the mags are tensioned.