Nice looking gun, looks like a European style target pistol or a more modern reproduction of one. The marking is curious, Remington was primarily a barrel maker in their early days. Not sure if they sold locks as a component along with their barrels though I believe some of their later military rifle locks were marked in a similar fashion Expanded into rifle manufacture and percussion revolvers later. All of their non revolver type pistols that I know of were cartridge guns and outside the venue of this forum.
The gun in the pics looks almost new or heavily cleaned and polished, perhaps someone added the Remington name to it for their own reasons? Could it be a reused or old component lock. Did the modern Remington company ever consider offering a muzzle loading pistol, perhaps as a nostagia piece? Curious. Any knowledge on where or who the gun in question came from? Are there any marks on the barrel? Perhaps on the underside. Might go a long way to clarify what exactly we are looking at here.