Four Fun Facts about the Oerlikon 20mm Antiaircraft Cannon!

[old tanker]

For what it's worth, here is some info for WW2 era ammunition:

20mm Oerlikon

"The fuse is not equipped with any bore-safe feature, and will act whenever the closing disc is displaced into the fuse with suffi*cient force."

http://pdf.textfiles.com/manuals/MIL...april_1994.pdf

TM 43-0001-27 ARMY AMMUNITION DATA SHEETS, chapter 14 covers 20mm ammo.
The M139 was a built under license Hispano Suiza 20mm cannon that had a long and unhappy life in the US Army on the M114A1. Glad I was not a Scout along the inter German border in those days, but fuzes were mostly bore safe by then.