7.62 ammo is illegal in France, as is any military caliber.
That’s why French shooters have to get rifles in non-military cartridges like .300 Savage and .30-30.
Just having that ammo in the building is a crime.
There are even Euro rimmed versions of military cartridges like German 7.92 (8mm) to get around these bans.
I suspect at least part of the weapons haul being “war grade” is a matter of the chambering.