Well, it looks like the barrels are smooth. I really do not know much about antique firearms. The butt stock opens at at the bottom so shot could be loaded- maybe two. The words Swinburn and Son are imprinted on the top of the barrel.
I have a Swinburn and Son double barrel percussion flintlock pistol and I cannot find any information on the web or otherwise on this pistol. It has British stamps and a belt holder on it as well. Any help would be greatly appreciated.