Sniper: Ghost Warrior

It will probably be difficult for you to find a legitimate game that's going to be any fun for you, because very few people play this game anymore, but you can boost it by having at least 4 people and setting up a VIP match on Camp. Set the time limit to max and the kill limit to max, then have everyone join your game. Each person takes a turn killing everyone else. The shooter sits at the top of the road in the middle of the map while everyone else runs to the road and gets picked off.
Make sure everyone gets an even amount of time to snipe. The match is 20 minutes, so if you have a group of 4, each person gets 5 minutes, etc. You will each get anywhere between 45 and 55 kills a game.

Exact game setting for host:

Ranked match: Yes
Match type: VIP.
Map: Camp
Public Slots: 6
Min players to start: (however many are in your group)
Reward limit: 10000
Time limit: 20:00

this solution is mostly the same as the others but instead of changing every 5 minutes let the host kill for the full match. The reason for this is because the host gets twice the amount of kills. for example you get around 60 to 80 kills in a match atleast until the point limit. and now comes the good part because of the fact that you host the game the kills count as double meaning you get twice the amount of kills instead of the regular 60 to 80 so you only will have to get 250 rifle kills for the achievement instead of 500.

this has been tested for the pistol kills and the 250 sniper kills and this works
the double host kills was pointed out by Redemption626 in the solution from SerjiTank who posted this in the solution for the 2000 kills

saves alot of time in my opinion

Ranked match: Yes
Match type: VIP
Map: Camp
Public Slots: 6
Min players to start: 4
Reward limit: 10000
Time limit: 20:00

I had to remove my other solution for this achievement because things have completly changed. It is very hard to find a public game anymore so your probably better off boosting. I have tried for a good 30 minutes to get into a game but no one plays this game anymore.

BOOSTING METHODS.

4 Players

Ranked VIP on camp.
Everyone run to the street running across the map
Take turn for 5 minutes each killing as much as you can.
Then rinse and repeat.

5-8 players.
Ranked VIP on camp.
Everyone run to the street running across the map.
Take turns getting to 32 kills.
Then rinse and repeat.

NOTE: THIS MUST BE DONE IN RANKED MATCHES