Summary
Carbine
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Compared with other examples of the Covenant's armory, the Carbine is somewhat unusual: its energy projectiles are fast and damaging, but its single-shot design seems strangely old-fashioned. Don't misgauge its strength, though. When used by a professional, the Carbine is an accurate weapon redolent of a cross between the Sniper Rifle and Battle Rifles.
The only Covenant weapons that use ammunition instead of a battery are the Carbine, the Needler, Fuel Rod Cannon, and the Brute Shot.
With a 2x zoom facility, it's possible to make lethal headshots from afar. The Carbine's only real shortcomings are that your position is betrayed by a yellow trail with each shot, and that its rate of fire is rather slow. When you get your hands on one, be sure to take advantage of it.
It is sometimes carried by Brutes and Elites, but most of the time they stick with their favored plasma rifles. In the hands of an enemy Brute or Elite, they can be deadly, however.
For an energy weapon, the Carbine appears, intriguely enough, to be more useful against Flood than the others of its kind.