the military teaches you how to shoot thier way so if your thinking of going in the military your of the age to do it you might as well go in and learn to shoot thier way
just know that a sniper job isnt a starting job and you will need to get slotted, this takes time if it happens at all and you have to be a top notch soldier for this to happen
if your wondeirng what a good sniper rifle is for a low cost look at the Remington 700P... if you just want a rifle for basic marksmanship check out the Ruger 10/22 you can get one for cheap and rebarrel it, get a bunch of aftermarket parts nad make an affordable tack driver out of it