After going through a good number of vests and rigs during my career as a sniper I have finally found the gear that works for me. It carries all of my magazines with ease, it has my hydration stored, and it holds extra bags of ammo, a container of propane, binoculars, my side arm, tools, and still has plenty of room for more. Best thing is that it is the lightest, most maneuverable kit I've ever seen.
This is Alice gear. Although it is a much old design than the ever popular MOLLE gear, I find it suits the sniper role perfectly. It is still customizable, you can attach a variety of different pouches wherever you choose but you don't need a bulky, hot plate carrier vest. The set up I am running with now consists of an H harness and a belt. All I need to carry everything is a butt pack, 2 canteens, and around 5 double mag pouches(6 extra pistol magazines and 4 extra rifle mags) all set up on the sides and back area of my belt; it doesn't limit your crawling capabilities in the least. You barely notice it. The entire rig is very comfortable; it is nice and snug so it doesn't bounce around at all.
Finding gear that will carry everything you need and then some yet is light and maneuverable as a sniper has been a challenge. From what I hear, most of the sniper community here and elsewhere would probably agree. I find that a nice, yet cheap Alice gear kit fills every expectation a sniper could want and I highly advise it to anyone and everyone.