I remember playin' with a weapon pack which I really liked. All I remember is the sniper rifle which was modified to have a redish-orangish blurry energy-like skin and dealt a lot of damage. :\ Any guesses?
That sounds like Zark, which is essentially a mod with sniper machine guns kinda of weapons, with ridiculously bright effects, high firerate, full precision and very high damage. I played a lot with those in the past.