There's more than one cartridge known as "380 revolver".
One of them is basically the same as 38 S&W and found in enfield top break revolvers used by the Brits in WWII era. These use a bullet diameter of about .359/.360".
There is a much older cartridge from approximately 1870s that was also known as 380 revolver. I've seen a few belgian made revolvers chambered for this cartridge. The bullet diameter is approximately .375" according to Cartridges of The World.
Which cartridge is your revolver chambered for?