Almost accident with a WWII bullet loaded with white phosphor

With my little cousin we did some metal detecting, in the hope to find some nice old coins.
No coins where found, but we did find a big bullet.
In this field I found previously several the same bullets as well as casing of it.
I offered him to clean up the bullet, and drill a hole in it, so he could wear it on a chain around his neck.

This is the bullet.

After initial cleaning with a wire brush, besides the casing.

After cleaning it with a brass wire wheel on my drill.

After polishing it.

At this point I tried to drill a hole in it, but it was not possible. With my best drill bits at the slowest speed, I could not even get a dent in it.
Being curious what this bullet was made of, I decided to cut it open in the length with my angle grinder.
I started at the back, working my way to the tip.
Almost at the tip, it started suddenly flashing with bright sparks, so I quickly moved away.
When it was done “flashing”, and my tool shed was aired, I checked what happened.

Whatever was inside of the tip, was burning so hot that it even melted a hole in the tip from the side.

I contacted a colleague who has a passion for guns etc. He asked me to check the backside of the casing.
After cleaning it, it showed SL4 on it.

He did some searching and found that this means it was made in St. Louis, in 1944, therefore used by the US air-force when they where firing at the Germans during WWII.
It turns out that this was a API round, Armour Piercing Incendiary.
The white phosphor in the tip is dangerous stuff, I was quite lucky nothing serious happened.

Moral of the story is, don’t cut old ammunition open, unless you know 100% what it is.

More information on the round itself and the casing can be found here: