In Fallout 4, you can refer to the following for the location of the sniper rifle in the early stages of Fallout 4:
After you have just obtained the power armor in the main line, there is a "first step" mission. Go to the direction of Shisongzhuang and wander around. You will find an enemy lair on an overpass and find two sniper rifles on the upper floor as shown below. Two The gun was in the same location.
