Learn to shoot accuratly with an AEG first being a sniper even in airsoft is not an easy task so much to learn and you need a good head for ranges, most other snipers i come accross can shoot but cant do the other important roles such as stay back, stalk, and be selective everyone is in love with the idea untill the reality kicks in and you find most people will ditch a sniper rifle for a AEG at some point during the day because they want the kills, for me its personaly im happy to wait all day stalk one person to have a satisfying reward at the end.
Sniper rifles are expensive and upgrades are endless scopes are plentyful if you want to snipe learn to hunt learn the scopes your going to use (personally use MILDOT) and yeah i know no many can get on with them but the people i talk to who dont get on with them generally do not know how to employ i properly, target shoot regularly i shoot atleast 3 times per week in my garden and i make notes in my DOPE book, dont expect to fit a scope to a rifle and shoot it dead accurate it takes alot of time effort and money to perfect the rifle itself so be pepared patience is required.
Personaly like what as been said before L96 is a good option bolt action much like the mausers Sr pro and SR93 easy to use load and fire goo accurancy and range, and i find personally using 0.30g BB's helps.