The Corinthian is an SMG Blueprint added to COD MW in Season 3. In order to get this weapon, you would need to do certain objectives. But before that, activate the given mission to enable the objectives in the first place. In order to do that go to Barracks > Missions & Challenges > Warzone Missions and select the mission shown below.
Mission name to unlock Corinthian Objectives
- Super Frenzied Shooting Hysteria
Objectives to get Corinthian
- Get 7 kills in a (1) minute, 3times.
- Rewards – XP: 2000 | Loot: Equilateral Emblem
- Get 3 headshot kills in a (1) minute, 5times.
- Rewards – XP: 2500 | Loot: New Heights Calling card
- Get 4 longshot kills in a minute, 3 times.
- Rewards – XP: 3000 | Loot: Diamond Up emblem
- Execute 2 finishing moves in a minute, 2 times.
- Rewards – XP: 3500 | Loot: Flying Skull Emblem
- Get 3 quickscope kills in a minute, 3times.
- Rewards – XP: 4000 | Loot: Henchman Fodder spray
- Get 3 point-blank kills in a minute, 3 times.
- Rewards – XP: 5000 | Loot: Corinthian Submachine gun.
So a summation of 6 objectives should get you your covered Weapon BP.
Thanks for reading!