Battleborn

Oscar Mike has the easiest Lore challenge set in the game and shouldn't offer too much difficulty in completing.
I've still taken the liberty in explaining about how to get all of them.

I AM LITERLLY MADE FOR THIS - Fire 50,000 rounds.
Whenever you hold your bullet fired count will go up. While the most straight forward of his Lores, this should be the last Lore you complete if you play normally.

FITTING IN - Deal 36,000 damage in a single match with Frag Grenades.
This is made super simple by grabbing the level 2 Helix upgrade that adds a napalm detonation effect to your frag ability. Shoot it at groups of enemies or at the bigger enemies with a lot of health.

SOMETHING TO UGLY CRY ABOUT - Deal 20,000 Airstrike damage while cloaked.
You need to be level 5 in a match and then you can press to aim an air strike barrage then immediately activate the cloak ability with . This will take multiple matches as the damage the strike deals is sporadic.

ON SIGHT INTERVIEW - Kill 500 enemies with Red Dot Sight activated.
This is the level 3 Helix upgrade, select it with . I don't think you actually need to get kills with your gun, any kills you get with the upgrade activated should count.

FROM YER BEST BUD - Play 5 matches with Montana on your team.
You could simply play a Story or Versus match to completion but a faster way is load up a Private Story lobby with one other player and enable Hardcore mode on the stage "The Void's Edge". You select Oscar Mike, they pick Montana and then once the stage loads you both run straight off the edge. No extra lives so neither of you respawn, mission ends and that means you played one match together. Rinse and repeat four more times.