This is not a hard achievement to get. Simple play the game and switch weapons once you get gold. It just takes some time. The other solutions are good guides on how to speed it up.
However if you really suck with a weapon, or just feel it takes too long, you can boost this. We used this method a couple of times and works quite well.
You need 8 players (You can do it with 6 players, but with 8 you don't have to deal with randoms. Also having 1 or 2 backups for no-show is recommended)
- Have all 8 in one Xbox live party chat.
- set up 2 lobbies
- Have the first lobby search for hardcore squad rush
- Once they have found a match, let the other lobby 'join session in progress'
Once you have all 8 players in one game, simple meet up near the com-station. One person per team can kill 2 people from the other team. The 3rd person has to be a medic so he can revive the other 2. (4th person should be killing the other team)
Some extra tips:
- When the ticket count reaches 4 or so, simple blow up a com-station. That will reset the tickets to 20 again.
- You can go for 50 or 100 kills per turn. (50 is silver, 100 gold). That way you don't have to count, simply wait for the silver or gold star to appear. Then switch to next person.
- Have a 2nd person also be medic. Once the 1st person is shot, the 2nd can revive him. Then the 2nd person gets shot and the 3rd person can revive the 2nd person. The syringe needs some time before it can be used again, so using this method can save little bit of time.
- When someone is being revived he will stand where the medic was looking (sort of). This will result in the person(s) being revived to slowly move around the map. You can counter this by having the medic crouch down and don't move towards the dead person. There can be some distance between medic and dead person. (Unless he's to far, than you still have to move closer as a medic) If done correct, the medic doesn't have to move at all and only has to press RT to revive.
- Have 1 person (preferably on the defending team) be assault. He can throw some ammo which both teams can pick up.
- When it's your turn to kill you can switch class by either have someone kill you, commit suicide (with a grenade or from menu) or ask someone on the defending team to die, select the weapon you need, then kill him and take his kit.
- When your turn has ended, you can simply take the kit from the person who's next. That way you don't have to switch class to medic again (and possibly wasting a ticket)
- If you don't have 8 players and there's a random in the game you can keep bugging him until he leaves. Kill him, then have someone on the same team revive him and kill him again. Revive, kill and repeat. Try to avoid team killing, you will be kicked out of the game if you team kill too much. (You can shoot him and hopefully he will kill you. If pissed off too many times he will be kicked out due too many team kills ;-) )
- If you get kicked/lag out of the match simply 'join session in progress' again.