Good on you for checking first! There are a few different cartridges that start with ".32" – they are all different lengths, and they are not interchangeable with one another. This particular cartridge, the .32 H&R Magnum, was designed in 1982, so we're going to guess your grandfather's revolver is not compatible with it. While it is possible that your revolver is chambered for .32 S&W Short, we would bet it's actually chambered for .32 S&W Long. That was a police cartridge back in the day, so a lot of revolvers were made for it. Please check the markings on the frame and barrel, and if that doesn't give you answers you may want to consult an expert before ordering ammunition. We hope this helps!