New Army "Caliber Configuration Study"

[Tony Williams]

I'd also suggest that four categories are needed:

IAR
LMG
MMG
HMG

Which raises the question of where the Bren gun would fit into that classification.

It was magazine-fed, and carried and used by one man, which would suggest it's an automatic rifle like the BAR.

OTOH, it had a quick-change barrel and the gunner usually had an assistant who would carry more ammo and also change the magazines more quickly than the gunner could - which suggests an LMG.

You can spend hours debating these sort of points, because there isn't one correct set of designations, and they are affected by how the weapon is used as well as by its characteristics.