A story about a weapons teacher at Hogwarts "no name yet please help with an name"

Oh sorry for not finishing techno aliens 2 i have been busy but i have been write this, a story about a weapons teacher at hogwarts

“Get down!”a voice yells, as a explosion rocks the building. “that was a close one” I say to my self trying to get up. As another explosion rocks the building as I am knocked to the foor again  Then I crawl on my chest to where I last left my rifle. Then getting up on one knee and putting the stock of the gun in my shoulder and looking though the sniper sight. As I pull the trigger to fire a bullet. I feel all the things as the first time I used a gun. The hammer falling onto the bullet. The gunpowder sparking, pushing the bullet out of my rife. As it leaves the barrel, I feel the speed, the wind, the angle of the bullet as it flies to a tanks fuel cap. Then next thing I know I and thrown down and the place going black and I think of words my mother told me “Son I cant make you go to see your grandmother but promise me this. After your time in the army, killing people. Go see her she lives up in Scotland but take the train it will be easier” “i promise”....