Question about 20MM round

Hello, I have a 20mm round that my Grandfather brought home from WWII and after trying to figure out exactly what it is unsuccessfully, I was wondering if anyone here would know more about it? The projectile has sort of a greyish paint on it.

It separates into 3 segments. The headstamp has a B inside of a diamond, as well as the numbers, 541, and 42, which I assume is the year of manufacturing. The middle segment has stamped into it MAT 58 1/42. And has what looks like unburnt tracer element in it? And the top most portion has the code 254HNNC671, as well as having a white film side of a little hole at the bottom. If anyone has any information about this cartridge, manufacturer, projectile type etc. That would be greatly appreciated.

It only let me post one picture, so here is the photo of the headstamp.

more photos in the rest of my replies as well for the protectile.

And here is that white film in the projectile tip.

Hello and welcome.

You have a 20 mm Oerlikon round.

Not my area of expertise but I believe that the grey projectile indicates HE-T (high explosive - tracer). The fact that it is empty is good (safe). Is there a cavity in the base of the projectile?
I don’t know enough about the fuze but those more knowledgeable about this will chime in.

There is a large cavity where the tip screws into the projectile, completely empty as shown in the third picture, however on the base of the projectile where it mates with the case there is a hole filled with mostly unburnt element.

Here is the base of the projectile where it mates with the case.