Gears of War

There isn't really any easy way to get this but i'll give it a shot

Ok, 100 kills with longshot well i reckon the easiest way to get this is by active downing then shooting the enemy again from a couple of steps away in warzone but then someone might steal your kills which sucks. Obviously if your good you can just heashot people which will give you the headshot achievement aswell. Just keep at it and practise.

If your trying to do this legit, it may take some time to finish! it is best to find partners (6 min.) to start a match.

You can set up a 19 round warzone match and take turns with kills. You can get about 30 kills in about 25mins.

You can also go for Headshots at the same time!

This isn't really a solution, more some advice for people trying to unlock the various kill related achievements as quickly as possible - at the end of every boosting session you should play a quick one round local match against a second controller before quitting to dashboard or turning off your xbox. I've done this and unlocked Seriously yesterday pretty much bang on 10000 kills. I've also unlocked all the weapon kill achievements after 100 kills.

I think what's going on is that sometimes, for whatever reason, the progress you make in the last match of a session isn't added to the various achievement counters. I first noticed this when boosting the 'Win 20 matches on map X' achievements - if I won 20 matches in one session the achievement would pop, but if I spread them out across multiple sessions I'd have to play 21, 22, sometimes 23 matches depending on how many sessions it took.

Of course, it's possible I've just been really, really lucky - there's no way I can prove this works. If people start trying this and it doesn't work out let me know and I'll take this solution down.

This achievement can easily be unlocked while suicide boosting on War Machine without delaying the match completion time. You do not have to join a separate weapons boosting session to obtain it. The player going for the achievement should be partnered with the player running to the torque bow.

When the round starts one player runs to the longshot and their partner runs to the torque bow. You do not have to meet up as both are ranged weapons, and can kill from across the map. While the torque bow is charging its shot the longshot should zoom in on their partners head slightly above the center of the face. The torque bolt will not knock the longshot out of zoom. After the sniper is hit with the bolt they simply pull the trigger for the kill. I have personally earned the achievement this way as have a number of the people I have boosted with.

Boosting is the best method for the weapon achievements as they are somewhat glitched and require more than 100 kills to actually unlock. Gridlock is the most common map with the sniper to get the achievement on and War Machine too. If you get a headshot as well for each kill then you'll get the headshot achievement too.

heres a few tips for you guys.
when people leave the session the remaining peoples kills DO still count.
if you don't have enough people to start the game (you need 6 or 8) you can invite a friend to help start the game and they can drop once the game has begun and the remaining 5 or 7 can carry on without them in the game as it doesn't matter.
executions kills do not stack with pistol or chainsaw kills.
the only 2 that can stack are the longshot and headshot achievments.
be careful with the pistol kills as if you are to close to the person getting killed it might register as an execution, you can keep track of this by watching the kill symbol that appears on screen when somebody dies.
the hammer of dawn achievement should be got on the dlc map garden as its a straight line from both sides to the middle and the hammer of dawn spawns every round, the only other map is rooftops but that requires a lot of climbing to get to the middle.
a good all rounder for weapons kills is gridlock not raven down.
expect each round of first to 19 round wins (37 rounds) to last 40-50 minutes each and you will need to do about 4 rounds in order to get 100 kills per person in a 6 person session, this will take about 3 hours to get 1 person 1 100 kills achievement basically.
not all kills are kept track of in the all time ranked stats screen in the menu, for example hammer of dawn is not on there, so make notes of what you need inbetween games as only 2 people can only get about 90 kills in 1 6 person game.
don't bother going for torque bow or grenade kills in your sessions as people do just those kills in boosting sessions for seriously and they are available daily on t.a. and you will get them easily in those sessions.
I think that's everything, I hope that all helped. goodluck.