FWIW, the "rechambering" involved inserting a short steel ring into the chamber to take up the space between the length of the 9mm Browning Long and the 9mm Browning Short or .380 ACP. That ring has given trouble in a few guns, even though the conversion works OK most of the time.
That pistol was intended as FN's answer to the Luger. They couldn't make the Luger, and designing an entirely new pistol was a bit much, so Browning scaled up the Colt Model 1903 to 9mm and worked up a new cartridge which was more powerful than the 7.65 Browning (.32 ACP) although not up to the 9mm Parabellum in power.
It was not a bad cartridge, but keeping to the power level that could be handled by a blowback pistol restricted it considerably. It was the last of the Browning semi-rimmed cartridges. At about that time, Browning saw or heard about the 9mm Parabellum (Luger), realized that supporting a case on its mouth was the way to go, and dropped the semi-rimmed idea for his last two cartridge designs, the .380 ACP and .45 ACP.
Jim