I’m not convinced its not a “.320” whatever that may mean in real terms. Being Belgian, home of the cheap pocket pistol in those days, makes it very credible as a Saturday night special load since a significant percentage of Saturday night specials were Belgian made.
I had better explain myself a bit more clearly. I’m not sure to what extent the ammuniton manufacturers of the day felt in any way constrained to stick to the dimensions used by other manufacturers. They also weren’t too particular about how they described them either.
There were no recognised industry standards much less international standards so if the round fits in the gun that was good enough. Most of these .32 pocket pistols were very loose in the chambers anyway.
So the fact that it doesn’t conform to recognised dimensions shouldn’t automatically rule it out as a “varient”. However, if it is a varient previously undocumented that would make it an interesting find.