Someone explain why the Swedish 6.5x25mm CBJ is capable of punching thru APC armor

Sweden’s 6.5×25mm CBJ round is no joke — it can punch through APC armor.

Even better, it shares the same dimensions as a 9mm, meaning most 9mm platforms can use it with just a barrel swap.pic.twitter.com/Hzdg5xtnqz

— Massimo (@Rainmaker1973) December 6, 2025

The round looks like the old Black Talon with maybe a titanium core. Is that enough to penetrate APC armor? If so then why aren't we doing it with 9mm? Why not with 5.56? Are we leaving solutions on the table cause from my chair the math makes no sense, the penetration is far too high on a round so small.