Two major factors that will get in the way of your perfect shot will be the distance you are from the target, and the wind.
The distance will of course make your bullet drop. Luckily you can match the distance at the bottom to the information of your reticule.
The same goes for the wind, which affects how the bullet moves horizontally. Again this will be specified on the left of the reticule, and you can match that to the reticule information.
Your sniper rifle will be good at first, but as the jobs get more complicated, so will the shots, and your rifle will need to be better.
Power and stability are incredibly important, and will make the difference in many missions. For cash or gold, you can upgrade these stats.
There are several levels to each stat to upgrade, but ultimately, there's only one way to get a rifle powerful enough for later levels.
A new rifle
Yep. You need a new rifle. In the arsenal tab there's a series of ascendingly powerful - and expensive - rifles for you to purchase.
It's simple, the pricier it is, the better it'll be for you, with more power and stability than the one before it, making those later missions much easier.
You'll know when you need a new rifle. Most missions will be giving you incredibly difficult shots, possibly even with bullet drop you can't even compensate for.
Honestly, I hate advising this. This is the worst advice I could possibly give. But here it goes. Sometimes, watch adverts.
Watching an ad after a mission will double your reward, and if you're really in need of a new rifle or upgrade, you can get those pretty quickly.
Yeah. Adverts. 30 seconds of them. You can skip at any time, but you'll lose your reward. I know. Harsh. But you will get cash for rifles.