Wonder who decided 25mm for the Aden from the earlier 30mm and why the Mauser uses 27mm?
Was the later to use captured Russian ammuntion or the other way about?
Was the change from 30 - 25 'cause it was 16% less therefore would save 16% in the budget?
Or were both space/weight saving?
But if 20mm was good enough for the world's largest air force was it necessary to specify equipment that could not be off the shelf?