The Novice and Veteran Capturer are very buggy. My Novice hasn't unlocked yet and neither has my Veteran Capturer. It has been reported that you have to host for the Achievement but the guys I boosted with got the Achievement when they weren't hosting the match. So This is basically on luck. But it is worth 0 so it isn't really a necessary achievement since it will not ruin your gamerscore completion.
You may choose Any Map, Any Time Limit (preferably the lowest), and Set the the capture points needed as 5. Now when you are in the lobby have everyone change there profile preferences from Yes to No on the Tank option. You will be able to choose a bazooka when you start the matcn, choose it and when you start just blow yourself up since you do not have to win the game you just need to have played 20 games.