Hi again Sarah!
The shrunk link below, started life as a six line link, so I hope it works! I was racking my brain to see what else we can try. At first I thought WW1 records, Ancestry, then I realised Willliam was too old.
Then I thought National Archives. If old William wasn't in the foot regiment you were given, maybe he's in another one.. I put the name William Burnett in the Nat Archives search engine and then clicked on Forces or similar.
In other foot regiments, in the Chelsea documents there are two possibles: William Burnett born Walton le Dale, and also William Burnett born, unknown.
I don't know if either are worth a try, I had a gggrandfather's Chelsea records. You van order online. Specify which part - all if it's short or correct family data or simislar if it's long and you get an estimate of cost in about 24 hours. then you can order online.
Mine took about a week, and for less than the price of a cetificate, I got a wadge of beautifully presented A3 sheets flat and protected by heavy card. still causes great excitement!
Of course, where was he discharged?? Carlisle Castle! He was born in Wimborne Dorset and enlisted down there. So it would be one one way your guy would have got to Carlisle!
The best of it is, can I find where he was in Carlisle or how he got to be married to an Irish lady in Wigan, no time later? No chamce and I live in Carlisle!!
There are a few slightly later military entries but mostly navy, and carpenter, so they don't really fit the next Wlliam.
Link's below.
You never know!
Best wishes
Emms
http://www.rootschat.com/links/03sx/