Warhammer 40,000: Space Marine

Almost all weapons have a challenge for Kill "x" amount of dudes. Use a variety of weapons and go for the easy challenges. The Tactical Stalker Bolter is a good one because it has get x amount of kills and get 5 head shots. 2 challenges in 1. A good deal. Also make use of your pistol as well.

Between the basic classes of Tactical and Devastator you can get this fairly quickly.

Bolt Pistol + Bolter + Stalker Bolter + Heavy Bolter = 5 quick challenges that don't require much effort to do. If you plan to play the multiplayer often this should come very naturally over the course of the game.

*Edit*
Fixed some weapon names for accuracy

This can all be done in Private Matches. This makes this ridiculously easy to boost, just going to take a while. The host can adjust the time limit, health/armor limits, score limit, and spawn times. This will be the standard for boosting all challenges:

Game Type: Seize Ground
Map: Waste Management
Time: Unlimited
Score: 5000
Spawn: Lowest Possible
Armor: 25%

Part 1. Multi-kills, Charged Shots, Melee weapons, mostly anything other than Kill Streaks:

Set up a group of 8 players (Maximum Xbox Live Party Size, for communication) and start a private match. Have 1 player be Space Marine (Team A); the other 7 will need to be Chaos Space Marine (Team B). (Or vice versa if going for kills as SM/CSM)

Perks: Team B spawns as Tactical class with Rapid Deployment on. Team A spawns with whatever weapons they are going for.

When the match starts, have Team B capture all of the points, and then meet at Capture Point B. This will be the new spawn point for Chaos. Have Team A start killing Team B while standing just outside the ring. With Rapid Deployment on, Team B should spawn in within just 4 seconds of dying.

With this setup, the score for Team B will reach 5000 at about 12-15 minutes; they will also receive a win. However Team A will get a ton of kills, knocking out challenges very quickly.

NOTE: Multi-Kills only count once. A multi-kill of 4 counts the same as a multi-kill of 2, just one time, so have Team B space out into groups of 2 when going for vengeance launcher and meltagun kills.

Part 2. Kill-Streaks done easy!

Kill-Streaks work like this. Kill 3 people, you have a kill-streak. Anymore kills after 3 is still 1 kill-streak. For efficiency sake, you want to die after 3 and start the next one. 300 Kills is easier than 1,000.

Same game type setup as above. Set up a group of 6-8 players and start a private match. Have 2 players as Team A, and 4-6 players as Team B. Can be done with just 4 on Team B, but having more makes it a bit easier, more efficient and more fun.

Perks: Team A: Homing Beacon, Rapid Deployment // Team B: Rapid Deployment

When the match starts, Team B captures all the points and meets at Capture Point B (CPB). Team A will consist of two players, The Kill-Streaker and the Spawner. Team B will have 3-5 players that will die for the Kill-Streaker and one player that will be killing the Kill-Streaker.
On Waste Management there is a bridge leading into CPB, this is where Team A will stand and fire upon the re-spawning Team B. One player, the Kill-Streaker Killer, will stand away from the rest of Team B (Behind the kill-streaker is probably best) and kill him after he gets 3 kills. At this point, the Kill-Streaker will re-spawn in on the other player’s homing beacon and start a new kill streak. You can get 50+ kill streaks in a match this way.

If you’re comfortable, you can actually have two people going at once for this on Team A, just make sure you don’t kill player before the other re-spawns. It is extremely efficient when going for the Bolter and Storm Bolter. The Heavy bolter is a one person at a time gun due to the fact that a Devastator cannot have homing beacon or rapid deployment.

To get this achievement you will need to complete all the weapon challenges listed below:
Bolt Pistol – 150 Kills
Plasma Pistol – 150 Kills
Bolter – 250 Kills – 100 Kill-Streaks
Stalker Bolter – 250 Kills – 50 Headshots
Plasma Gun – 200 Kills – 100 Charged-Up Shot Kills
Meltagun – 250 Kills – 36 Multi-Kills
Vengeance Launcher – 250 Kills – 36 Multi-Kills
Storm/Twin Bolter – 250 Kills – 100 Kill-Streaks
Heavy Bolter – 250 Kills – 100 Kill-Streaks
Plasma Cannon – 250 Kills – 36 Multi-Kills
Lascannon – 250 Kills – 100 Extreme Range Kills
Chainsword – 250 Kills
Power/Chain Axe – 250 Kills
Thunderhammer/Daemon Maul – 250 Kills

Note:
Multi-Kills: a multi-kill of 2 is the same as a multi-kill of 5. Only counts as 1 multi-kill. Weapons that use this as their Skill Kill Challenges require a total of 36 multi-kills.

Kill-Streaks: a kill-streak of 3 is the same as a Max-Kill-Streak of 10. Only counts as 1 Kill-Streak. Weapons that use this as their Skill Kill Challenges require 100 separate kill-streaks.

Extreme Range Kills: These are from practically across map. A medal will pop up with each one that signifies a “Long Range” kill, or something along those lines. This helps with keeping track of this, and what counts and what doesn’t.

Headshots: A little icon will show up next to the points awarded for a kill signifying a headshot (a skull in crosshairs).

Power Sword: Is it needed? No! You do not need the Power Sword obtained through Kill Team to finish this achievement.

Hope this helps with the task of beating all the challenges. If you think I should update/change anything to make it faster, just post in the comments.