Plastikosmd,
My thoughts on your very nice late French FL pistol:
Lock: Nice late FL. Great condition. The signature is a puzzle. "D Sedan” makes sense. It’s a city in NE France. I think the signature starts with an “L”, or less likely a “T”, but probably not a “J”. Der Neue Støckel lists 45 gun makers in Sedan, none of which I can make fit.
Stock: Although broken, bondo’ed, maybe shellac’ed, and possibly the accidental recipient of paint overspray, the checkering is in unusually good shape, I like the architecture, and the piece appears well made. Looking at the lock mortise just above the sear spring area, I see open grain, suggesting the usual walnut. I would hate to see that fine stock replaced. It could certainly be restored by the right hands, leaving the valuable original parts and history intact.
Barrel: Gorgeous swamp and rifling! Striping in some images looks like (faux?) Damascus. When you make the new breechplug, please don’t change the female threads in the barrel. Match the plug threads to the barrel. I agree the numbers look relatively recent. Maybe "bondo man" put his "mark" (last four of SSN) hidden under the barrel? If you know who owned it in the past, you might corroborate that.
You have a nice pistol, well worth restoring and keeping as close to original as possible. I agree it would be fun to shoot with light loads. Upon discharge, my 69 cal multigrooved French officer's pistol with 30 grains fffg powder twists fairly violently in the direction oppisite to the rifling twist. From my experience, if you shoot it in a restored stock, use VERY light loads :-)
Bill Paton