4eme categorie (4th category): defense and target firearms if I remember right. Basically revolvers in 32,38,357,44. Semi autos in 38 super, 40, 357Sig. Whatever is not 1st category.
Anything chambered for a caliber that was used by the military falls into the first category named "armes de guerre" loosely translated into "war guns" that includes 9mm, 45acp and even 32ACP.
It's a lot more complicated than that and I'm sure Breizh (Btw...Kenavo!) will correct me if I'm wrong. It's been a while since I've studied the french laws, thanks to the 2nd I'm not concerned anymore...