i think there was an issue with the video-game or server.
i just got back from another round and the counter went up by one. so i think i'm good.
UPDATE:
- last night i played about 20 games with the required gun+frangible-wounding and got about 20 kills each game
- but none of them counted towards the in-game counter
- today i log in play two games and both counted up from 3 out of 5 to 5 out of 5
- so i got the in-game challenge!
i don't know what changed but i think there are two possible reasons:
- game doesn't let you progress 5 out of 5 in one day
- game servers for some reason did not save my progress (which i've seen talk of...)
i don't know which reason is correct. both are just speculation.
but the important thing is that to get this perk you just need to have the weapon and the "frangible-wounding" and do 5 matches and get 3+ kills with the weapon in each match.