Codex Entry

 The Claymore used to be a hard-hitting but poor-selling shotgun due to kickback problems snapping the arms of anyone but krogan firing the weapon. After a rehaul of its kinetic dampening system, the Claymore is being rolled out again. As a way to lure back customers, the gun's manufacturer has lowered the shotgun's selling price without skimping on its stopping-power.

Weapon Acquisition

 Single-Player

  The Claymore can be found during Attican Traverse: Krogan Team, shortly after meeting Grunt. If you fail to find the weapon, you can purchase it after the mission in Cipritine Armory.

Multiplayer

  Awarded at random as a rare-level drop.

Weapon Usage

 The M-300 Claymore is the heaviest and most powerful single-round shotgun in Mass Effect 3. Due to its high weight, low ammo capacity, and slow reload speed, careful leverage of the weapon is necessary for success.

• The Claymore's enormous damage and slow reload speed make it the perfect weapon for reload cancelling. When properly reload-cancelled, the Claymore becomes the highest damage-per-second weapon in the game.
• For weapon-oriented Infiltrators, the Claymore can present the highest damage potential for close-range combat. Tactical Cloak, when built for weapon damage, allows the Claymore to kill any human-sized enemy on any difficult in one shot if it is aimed well. Tactical Cloak is also an excellent power for reload cancelling.
• The Claymore is probably too heavy to be effective on power-oriented classes, except for the Vanguard. The Vanguard can compensate for the Claymore's weight either by using Nova: the recharge speed evolution of the power decreases the effects of carrying the Claymore, while the Half-Blast evolution allows enough invincibility frames to survive until Charge has finished cooling down.
• The Soldier can use Adrenaline Rush's instant reload to essentially fire two Claymore rounds at once, which will level most enemies on any difficulty.
• The Claymore benefits enormously from Armor Piercing Ammo, which allows it to punch through Guardian Shields and do increased damage to armored enemies like Brutes and Geth Primes.
• The Explosive Burst evolution of Incendiary Ammo can increase the damage to an enemy's armor or health by a huge amount, usually eliciting 4 bursts per Claymore round.
• The Claymore, being a shotgun that fires eight pellets at once, is excellent against all enemies with Shields or Barriers, as it effectively ignores the shield gating mechanic even on Insanity or Gold.