Obviously made in Belgium from the initial viewing of the ELG proof stamp and of course the "Made in Belgium" stamp. The 14.7 indicates the bore diameter to be 0.579" or 24 gauge. There is a manufacturer's hole for drilling the flash channel that will have to be plugged. Is the hole threaded? You will have a "clean out" screw for that breech. The breech appears to be a chambered breech with the flash channel in the breech plug.
I don't see any markings on the lock. There is probably no fly in the tumbler. Is there a half cock notch? Earlier smooth bored guns may or may not have a half cock notch. Probably made early in the 20th century or late 19th century. Does the lock function?
I'm afraid I'm not much help in identifying your barrel.
A barrel like this was made literally by the hundred thousand in the ateliers des armes in Liége, where this barrel was made. ELG = Épreuve Liége = Liége Proof House. The 'Made in Belgium' stamp is slightly unusual in that I have never seen such a stamp before - usually the ELG makes it obvious enough. To me it looks very much like a US import stamp - it has the style and font associated with that kind of mark. Also note that it is off-set - no self-respecting gun-maker would suffer such a thing to leave his workshop.
My goals are making a shooter and a hunting piece. I love black powder rifles but I'm not tied only to traditional pieces. So any ideas both traditional, modern, or hard lessons learned that I can work into a fine weapon.
I think toot may have the right idea.... Belgian companies were still making muzzle loaders for African trade when the revival of US interest in the old guns really began to take off in the 50's and early 60's. US import laws of the time required a "country of origin" stamp. Stoeger, Dixie and others bought guns from Belgian firms for import here and they would have needed the import stamp (Liege proof marks not being adequate for identification under US import regs). Probably came off one of those old imports.