How many victories in all do i need for mastery? Any tips for the concussion rifle mastery ( half way there but i don’t see it anymore 
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Flood Victories are the same amount as your Dominion Victories were. With the Flood Victory Commendation, you have to be first place (highest score at the end of the game; Ties will not help) to rack up the Commendation.
For Concussion Rifle, the map Perdition (in the Castle DLC playlist) helped a lot, but I finished up the Mastery in the Fiesta gametype (not the Classic version) and the Lighting Flag gametype in the Action Sack playlist.
Camping with the weapon will help. It’s not a rushing weapon (especially now with the weapon tuning). It takes 3 direct shots to kill someone (though even the slightest of lag can affect how many direct shots it will take).