I have a book about the history of Remington and old Elias made a bundle making barrels for other makers. I have an old original gun with a barrel stamped Remington. It has a Goulcher lock.
There were some very rare double and triple shot single barrel guns made in the early percussion days. A shooter would load two or three loads one on top the other and there would be more than one nipple a few inches apart to ignite the lead charge and then the next rearward nipple would be fired. A few decades ago, at the Allentown (PA) Gun Show, I saw a pistol with 4 nipples and a sliding percussion lock that would slide along the barrel to line up with the nipples. There were all manner of problems with such guns. The loads had to be just right so the powder charges lined up with the nipples, the patch ball wad combo had to be rather tight to keep the flame from reaching back and igniting the next charge back etc.
But there were indeed double shot single barrel percussion guns.