This is quite a coincidence, I'm researching a soldier in the 40th Regiment at Waterloo who was a friend of WAC. If you go into this link which is the History of the 40th, you'll find him mentioned. The guy I'm researching along with WAC, joined the 40th at 16 and was an ensign at 17, WAC probably did the same. He Joined Jan 1814.
https://archive.org/details/historicalrecor00smytgoogAlso there is a Waterloo roll call online as well, his record is on there, it is
http://www.napoleon-series.org/research/biographies/GreatBritain/Challis/Images151-200/151.pdfI have him stationed in Stirling Castle in 1817. It might just be another friend who was at Waterloo with him was an assistant Surgeon and might have been the one to amputate his arm.
Hope this helps,
Stewart.