I gleaned a little from Gunboards, including this: “[PR] was the mark used by Fabbrica d'Armi Esterina Riva for their black powder replicas line, imported by FIE (Firearms Import Export).“ I seem to recall seeing PR together with FIE on at least one revolver I looked at and one commenter on Gunboard said that the PR is usually seen together with FIE, but I’m only repeating what others said.
May we know the model of your revolver? Year of manufacture? More pictures? How much did you pay? What’s your adjusted gross income? (Don’t answer the last two questions - they are a joke, intended to make someone smile.)