If there was one thing that Harry Potter was when he really needed to be, it was patient. That's not to say that he didn't act impulsively at times when was younger. Harry was a teenager after all and therefore needed to be granted some consideration. However when he truly knew, deep-down, that self-restraint was necessary for the success of whatever the task he was undertaking, Harry was a master.
Years and years of hard labor under the Dursleys and months of being locked in his room with nothing to do had forced him to be able to dissociate into this certain… state of mind, if you will. Using that frame of reference, it is easy to understand why Harry was able to tolerate his body's current, uncomfortable position for the past several hours.
Lying on one's stomach is not the most horrid way spread out, but doing so atop the Astronomy Tower at Hogwarts School of Witchcraft and Wizardry could be one of the most horrid places to be in. All in all, it was a matter of personal preference. Harry, who had no qualms about doing risky things to achieve his goals, found the tower to be the perfect location.
"So are you sure this is going to work Harry?" a muffled voice from inside his robes asked. There, a two-way communications device similar to the one Sirius gave Harry long ago was tucked into his right-breast pocket. While it allowed for visual conversations, if one simply set the mirror side faced down on some surface or merely held the mirror away from his face, then conversations would be just verbal. Albeit, the person on the other end would still be receiving the images reflected in your mirror and you theirs, so one must be careful where one pointed it.
"Yes Hermione." Harry sighed as he glanced from his focus. "We've tested it, and it works. Just relax."
He returned his gaze back into the scope of his modified sniper rifle. Privately, Harry loved the thrill of holding it. He would never admit this to anyone, but it gave him a certain measure of confidence learning how to fire a gun. Now came the risky part: shooting. Hermione was very careful with the placement of the runes that would allow him to stick to the roof of the Astronomy tower, but even if one of them were out of place, the force of the recoil would overpower them, sending Harry over the edge and to his death!
That would be a pity after all this hard work, Harry thought to himself as his target marched up to the front gates. From his position, the target— Voldemort—was the size of an ant and looked completely docile. Fortunately for Harry, the modified weapon fired charmed bullets that would slightly alter their course to hit their target.
Such an idea had never reached the wizarding world. Spells were fired by hand, and therefore needed to be aimed by someone. As such, in order to be as accurate as possible, long-range dueling was not suggested. There were no snipers in past or present wizarding armies, just guerilla soldiers! Voldemort had planned for such a defense, unaware of the long-range capabilities of muggle firearms.
Harry focused the knob on the scope, pulling Voldemort's pale, bald head into view. With barely a twitch of his finger, a powerful banishing charm was activated and the war was over. Harry listened carefully, and was somewhat fascinated with the nearly inaudible 'pop' that resulted from his target's face caving in.
"It worked Harry!" The excited, albeit still muffled, voice of Hermione cheered from the mirror as bits of Voldemort's brain leaked onto the grass.
"I can see that!" Harry chuckled in reply, slowly dismantling the rifle and tossing the components to the waiting set of hands of Seamus Finnegan peeking out from the window. Seamus's father was eager to help, and without the Ceannasaí's help Harry doubted that such an operation would have gone as smoothly as it did.
After carefully climbing down face of the tower and jumping through one of the windows, Harry glanced back outside to watch the Aurors capturing the confused Death Eaters that hadn't yet escaped. It's finally over, Harry thought to himself. It's finally over.