Handwritten instructions and drawings on the use of a rifle

My father , Sylvester Foran, was born c.1892 in Dublin and worked in the G.P.O. (General Post Office). He enlisted with the Irish Guards when war broke out and trained in a barracks in Brentwood, Essex. He fought in France and Flanders - Verdun, Ypres, Vimy Ridge.
We have many war stories about him. He was wounded twice and buried alive once when a trench fell in on him. He was rescued when somebody saw his leg and pulled him free. He avoided the Somme after this last incident. His Commander - who became General Alexander - once rescued his platoon when they were caught behind enemy lines. He had a bullet wound he used to show off. He finished out the war. He was in the military police for a time, and then joined the prison service.

I have a letter from the Irish Guards, with their letterhead and some postcards. The page with instructions on how to assembly a rifle looks like his own handwriting. The bag was one given to all soldiers for their correspondence. In the group photograph, he is in the back row (standing), 2nd from the right.