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First of all, perks are upgraded by completing a series of perk challenges. To get a perk uograded to "pro", you have to complete 4 of the perk challenges. So, to get Overkill Pro you must complete the challenge called Overkill Pro IV, which is completed by getting 120 kills with your second primary weapon.
to put what he said in english, get 120 kills
You get 100 or 200 kills with your second primary weapon
You need to get 100 kills with explosions with danger close equipped
Yes, when playing MW3 and you have a specialist and you unlock a certain perk so many times it does become pro.
in any call of duty game with perks, you can unlock the pro "improvement" by creating a class with the perk you want and play with it some time. after getting a certain amount of kills for example you will get the perk improvement
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To unlock the all pro emblem you must acheive this ... get 2 headshots with 1 bullet.
by getting close range kills
Unlock system
120 kills with sleight of hand on
in order to unlock warlord pro in call of duty: black ops you must complete these series of challenges.150 Kills using a gun with two attachmentsGet 10 Frag or Semtex KillsGet 1 Multi-kill with Frag or Semtexonce all of the challenges are completed you must purchase the pro version for 3000 cod points.