Actually the .327 Federal magnum, the .32 H&R magnum and the .32 Long are all the same caliber. That is why you can shoot them from the same gun. They are all .327" or .327 caliber.
They are, however, different cartridges.
Be very careful when you try to come off like an expert... not a dang one of those cartridges is .327". Matter of fact, I don't actually know of any chambering out there that is .327".
All of these cartridges are .312".