My grandfather was also in the Machine Gun Corp in WW!
I was lucky enough to find his service records had survived the war BUT there is very little on there about the MGC part. In fact there is a section with approximately 9 months with no information (October 1916 to July 1917) .............. the record jumps from when he was transferred to the MGC, and then boarding a ship in Bombay to get to "Mesopotamia" which is basically the Iran/Iraq area.
I have discovered that the MGC has lots of secrets tied up with it. It was set up in 2015, and took infantry men who were good with machine guns, whether that be from battalions in the field or straight out of training, as happened to my grandfather. But it is what happened after the war that is very strange. The MGC was disbanded in late 1919 or early 1920, and the records stored at Battalion Headquarters near Folkestone, but there then was a fire in February that literally destroyed every single piece of paper.
A group of 100,000 men and officers formed and then disbanded, and almost nothing to show for the fact they did exist.
It's very hard to find out where the MGC Battalions fought, although I have records of my grandfather being in and out of hospital in Baghdad and Ramadia with minor injuries and then flu.
Unfortunately, my mother's younger brother inherited all my grandfather's medals, photos and whatever documents he had, and I had already moved to Canada. After my uncle died, his wife burnt everything without contacting me .......... I was by that point the only grandchild alive as my brother had died a couple of years previously. We had been the only grandchildren.