The plasma rifle

A plasma rifle is a Covenant directed energy weapon that uses superheated ionized gas called Plasma instead of projectile ammunition. The weapon has a power output of 100-150 KV @ 2~3 dA, and can fire 360~540 rounds per minute. Unlike the Plasma Pistol, the plasma rifle is capable of semi-automatic, and full automatic fire, this is thanks in part to its dual plasma collimator design. Placed atop one another, these collimators fire in a "stagger" taking the slow automatic fire of each individual collimator and combining it, this design allows a faster rate of fire and more rounds per second, which adds to the lethality of the weapon. The Type-25 DER is the primary weapon of the Covenant’s officer corps, used by Elites and Brutes, although Jackalsand Grunts have been seen using this weapon, but not as common. Against UNSC infantry, the Type-25 rifle's lethality is considerably greater than its counterpart the Type-25 pistol, due to the faster rate of fire, injuries inflicted to the victim are severe third-degree burns, with the wound being cauterized instantly upon impact. Even near misses will produce severe burns and heat trauma. Should the plasma impact an object, the impact can create fragments that may come into contact with a victim, with a crippling or lethal effect. Generally two hits from either a plasma pistol or plasma rifle will kill a light, or non armored target. Like its counterpart, over extended periods of firing can overheat the weapon, causing it to become unusable for a short period of time. In the context of the Halo games, all of the plasma weapons' strength and lethality are compensated for both the sake of ESRB rating and gameplay. The Covenant boast a large arsenal of weapons: Most of them plasma-based. Most of the Covenant's weaponry uses a form of magnetic channeling that the human race has only applied in the MAC gun aboard starships and the Warthog-mounted M68 Gauss Cannon and the M99 Sniper Rifle.

Plasma-based weaponry is very effective against energy shielding and body armor. The amount of shots that can be fired tends to be very high, but power cannot be recharged and by firing many or powered shots in a short duration can cause the weapon to overheat, which reduces energy efficiency as well as forcing a temporary cooling period in which the weapon cannot be fired. Once the plasma reserves are used up, the weapon is useless except as a melee weapon.I got this information on halopedia.com