Yes, I am tackling the subject of sniping. I have little knowledge of it. But I have a great idea about it. I am giving ideas and tips I think could help:

1. Not every weapon could do this. It is obvious. Shotguns can't. That is why buck shot is the default round for that type. For the accuracy of the weapon, buck shot would hit at least one pellet at short ranges.

2. Sniping in movies is not the same as sniping in real life. How I know? I watched sniping television shows talking about the snipers in incredible missions. And part of the show, they describe the calculation and aiming. 

Aiming a target in the cross-hairs is usually at shorter ranges. Longer ranges, they aim higher and to the left. Why? The bullet do drop over time. Gravity. And the spinning of the bullet moves it to the right. Therefore it is done so. How much is based on distance and movement of target.

3. No scopes. This one is difficult, not impossible. This means the range of the shot is cut down by the accuracy of the iron sights and the talent of the sniper. Besides, in the American Revolution, snipers did shot with longer barrels accurately.

4. Pistol sniping. Obviously the distance is limited by the pistol. However it is possible down a long hallway. Aiming down the sights in pistols is safe. Not enough distance for much a bullet drop. Not enough for a measurable amount, anyways.

5. Gun maintenance is important. You can't shoot if your gun is jammed.

That is all I can share for today. I know there is a lot more about it. But I am giving you these tips to help improve stories with sniping included to be more believable.