The Astra model 400 in 9mm Bergman/Largo has been safely fired with the .380 cartridge and the 9x19 as well as several other 9mm/.38 rimless or semi rimmed cartridges, this being a blowback pistol relying on a extra heavy spring rather than a locked breech recoil operated autoloader.
If the extractor holds the rim solidly the firing pin should reach the primer.
Chamber dimensions of individual pistols will govern whether the cartridge will chamber.
Downsides are that if the case is pushed deeper in the chamber by the primer cup on ignition then you might get a blown primer, or the casehead may slam back against the breechface hard enough to break a firing pin tip or damage the breechface or extractor slot.
So while this combo may pose no danger to the shooter, it may cause damage to the pistol, at least if done repeatedly.