Oerlikon 20mm Antiaircraft Gun

Four Fun Facts about the Oerlikon 20mm Antiaircraft Cannon!
It's not often you hear any details about a big gun. Oh, they'll give you all the gross specifications like height and weight and caliber, but any more than that and you risk boring your audience. I mean really, if you are showing any kind of big military weapon to, say, well anyone, their reaction is going to be 'Oh wow. That's a big gun.' and that kind of fills the mind. You really don't want to intrude on that moment with bunch of numbers.

I've heard of this gun before, and I've run into that bit about how they sold guns to the Axis and the Allies. Okay, maybe not sold, but the same gun design was used on both sides.

The muzzle in the video makes it look like the barrel is paper thin. I think that maybe there is a flash suppressor on the end of the barrel.

The mechanism is a little curious. It sounds like the chamber is cylindrical. Usually they are tapered to make extraction of the spent cartridge easier. So the chamber is cylindrical and it is longer than the shell. The cartridge is inserted in the chamber and when it is fully inside the chamber and is on its way forward, the charge is ignited. It only takes a millisecond, so the shell better be all the way forward by that time. Now the explosion pushes back on the bolt (that is headed forward at a zillion millimeters per femtosecond) and the 400 pound recoil attached to it. At the same time the explosion pushes forward on the bullet, but the bullet may not be fully in the lands at this point. Remember, the extra-long cylindrical chamber? I suppose you could make the bullet the same diameter as the shell, and start the lands just past the farthest reach of the leading edge of the shell.