The Napoleonic and Peninsular Wars have been a particular interest of mine for years, so I was intrigued to read the above.
By my guess, if his skeleton was found close to Mont Saint Jean, if he was British, (in that position he could equally have been Dutch), if he was an infantryman then he may have belonged to the 30th.Regiment of Foot (Cambridgeshire). If that was a rifle (more likely a musket) butt, I'm surprised he was allowed to carve great chunks out of it! Lots of 'ifs' isn't there?
"Gæð a wyrd swa hio scel, ac gecnáwan þín gefá!": "Fate goes ever as she shall, but know thine enemy!".
I can teach you with a quip, if I've a mind; I can trick you into learning with a laugh; Oh, winnow all my folly and you'll find, A grain or two of truth among the chaff!
(The Yeoman of the Guard ~ Gilbert and Sullivan)