I'd recommend using frag grenade over snipe whenever you can. It'll keep up your electrified railgun stacks, and actually does more damage than snipe because it applies a stack of electrified railgun.
In addition frag grenade is an instant cast over snipe's 1.5s channel.
On a different note, snipe costs 15 energy in both MM and engineering if you're playing your class correctly. (As followthrough lowers the energy cost of your next 2 snipes by 5).
Virulence works well, and I'd suggest trying to Line of Sight (LoS) your opponents whenever you're applying your DoT's/Weakening Blast. Going up against any class that needs to channel (MM sniper perhaps?) they wont be able to put any real damage on you while you're dotting them up, and then when it's time to cull you'll put out WAY more dps then they will.
Apart from that remember to familiarize your defensives, and know what they work against!
Happy hunting!