If he lost a leg there should also be a pension record available. Ancestry are doing a free 3 day view of ww1 records 10-13 november. They also do a free 2 week trial, you have to give card details but if you cancel within the time it costs nowt. Be warned it is addictive and the time flies by.
There may also be a record of service at the National Archives at Kew, officers records are better preserved than other ranks. If you can't get there people do research, 1914-18 forum or long long trail offer these services.
I would have thought his time at the munitions factory would have been by way of inspection and liason between the army and the company running it. problems with shell quality was an issue throughout the war.