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
Just reach rank 47.
You unlock Claymore at Level 53 in MW3! :-)
Because in C.O.D MW3 all of your kills count towards kill streak rewards. For example if after you killed the right amount of people to unlock the pred missile you can unlock the next award in your kill streak set with kills gained from using the Predator missile. Hope I helped.
Yes, when playing MW3 and you have a specialist and you unlock a certain perk so many times it does become pro.
find the custom class and unlock them
"Colored guns" or gun camos (short for camouflages) are unlocked through normal weapon use - by getting kills or destroying enemy support and equipment.
I think you have to get 55 kills
After 50 kills with a single FMG9
As Special Ops in MW3 has it's own ranking system you may unlock call signs in there however, they will not transfer over to the actual online lay as the criteria to unlock them is different.
Get 3 kills in one life with your secondary weapon