Telling the difference between a machine pistol and a compact SMG

[AdAstra2009]

Really I don't think That you can really distinguish between Machine Pistols and Submachine guns.
The way I see it is that a Machine Pistol is a subcategory of submachineguns.

To put it bluntly

All Machine Pistols are submachine guns...But not all submachineguns are Machine Pistols