Dingus
How did it go? I see your post is a while back so you've probably been merrily shooting this for a while now.
I've picked up one of these too and plan to shoot it as well. I'm having trouble finding any good information on them. They seem to have been produced in Liege from about 1810 (the start date of the ELG in oval proof mark), and were exported widely. I understand that they were still being produced in mid-century, and could still be bought 'new' - probably made up from old parts in store in Belgium - later in the century and beyond.
What are the proof marks on your barrel? Mine has the little oval containing E over LG over star, and, separately, a tiny intertwined EL symbol (eprouve a Liege, I think). There's also a little crown over L, something that might be a star over an oval, and also a PP. There's no 'perron.' I think all of this might mean the barrel was proofed circa 1853-77 when the inspector's letter plus crown was used. I understand that the intertwined EL symbol for provisional proof was only used after 1853, but I may be wrong and it may be found on earlier barrels. The PP might be a maker's mark, or maybe an additional foreign proof? There are no markings visible on the lock, which is the typical rounded lock seen on these pistols.
I collect 18/19 c military guns and my assessment of the condition and wear on my pistol is consistent with earlyish-mid 19th c original, rather than a late 19th/20th c made-up pistol, though because these pistols might have been made up from old parts (I can't imagine the Liege gunsmiths remaking flintlock pistol parts in the late 19th c by hand, for example), it may be hard to be absolutely certain. I believe that 'mid 19th c' Belgian percussion pistols and revolvers were made up from old parts in store in Belgium in the 1950s and 60s when interest in muzzleloading/BP was beginning to take off again in the United States, where they were marketed.
Any further info or ideas on these 'Belgian Sea Service Pistols' would be much appreciated, as there is very little definitive written about them that I can find - but there are quite a few of them always being sold in the UK and US and they are relatively affordable, so more should be known!