I put togehther a collection of ~13mm HMG bullets.
Based on the size of the rounds, it’s very likely for the FN 13.2mm HE bullet to contain 3.5g (3x1.17g German 13mm cavity) explosive filler.
However the Swedish HE-T, made in Italy, that supposedly contains 3.2g Tetryl according to some Swedish military documents, can only contain 2.3g (2x1.17g German cavity size) based on my little collage. So I find the 3.2g figure somewhat unlikely, like the numbers were mixed up.
I’m sure it went down like this:
Sweden: Oh no, Germany invaded Belgium. Now how can we get our hands on 13.2mm explosive rounds?
Italy: I can make some ammunition for you Sweden :)
Sweden: Oh really? We would like to have some explosive-tracer rounds though. And the fuze should have high bore safety.
Italy: No problem, we can make some explosive-tracer rounds that contain 2.3g explosives with this very safe fuze.
Sweden: 3.2g explosives? Wow, that’s almost as much as the round without tracer.
Italy: I meant… never mind. Yes, 3.2g explosives :)
Even the Russian 12.7mm MDZ-3 bullet contains at most 2.8g explosive filler (I converted the incendiary to explosive filler). As you can see the round is smaller but there was a tracer variant that simply extended the shell and brought it back to the same size as other 12.7mm bullets that have a similiar lenght as 13.2mm Hotchkiss bullets.
And the Russian bullet achives that amount of filler thanks to the very short air compression fuze.
