I have a couple of those unknown projectile, the diameter is 5.9mm, length is 1.8, weight is 3 grams. It has a steel core at the tip and the rest is lead, open base, the jacket is magnetic.
Are you from China？This is Type 92 5.8mm pistol bullet
I’m not from china but I do get it from China! It’s from a Chinese keychain and I just pull the bullet out.
Was it in a cartridge?
If so, can you post photos of the headstamp- if possible- and a side view?
I don’t think it’s a matching cartridge, the cartridge is a 556.