Gears 5

This is the fastest way I’ve found to get the kills so far. If anybody has any faster ways then I’ll update the solution. Go to a Private Custom match and select Online Game. Pick the map called Checkout and game mode King Of The Hill. These are the settings you want:

KING OF THE HILL OPTIONS:
Fill with Bots - ON
BOT difficulty - BEGINNER
Rounds to win: (1 round is 15-20 mins on average so select as many as you like with that in mind)
Round score limit: 270
Execution Rules: OFF
Respawn time: 5 SECONDS
DBNO time: 3 seconds
Friendly fire: OFF
Weapon reapawns: AFTER PICKUP
Gameplay tuning: ASSIST ENABLED

WEAPON SUBSTITUTIONS:
Replace the Retro Lancer, Overkill and the Boltok for Salvo or any heavy weapon of your choice I suppose.

I found 5 enemies a bit much to deal with. They’d group together too frequently and I’d end up getting killed by one as I kill his buddy joined to his hip. For this reason, I locked off one enemy AI and played against 4 of them. All my team mates were locked off as well. So now that you have a 1v4 game set up, do the following:

You will be heading to the cupboards/toilets on either side of the map. You can see where this is because it’s where the salvo will be spawning for you now. You want to camp in here and leave the AI to capture the points and they attack you endlessly.
I can manage 600 kills per hour doing this. I grab the salvo, stay at the back of the room and I shoot it as they appear. Once the salvo runs out, I switch to the shotgun and I hide behind the wall (as shown in the video’s below), popping out to kill each enemy running to me. They keep coming at a fast pace so you can rack up the kills about as fast as you could ever hope for.
When you die (and you WILL die eventually), then head on over to the nearest cupboard/toilet and repeat. This will usually be the opposite side from where you just died of course.

I have made 2 videos to show what I do, depending on what side I spawn at. When I made the videos, I had been using the Tri-Shot, but after trying Salvo, I see that’s the better choice of weapon to have spawn in these rooms with you. Here they are:

This video shows the preferred side to be at and exactly how I go about doing it, as well as showing that I’m getting 100+ kills in 10 minutes:



This video shows an example of how to deal with the opposite side when you spawn there:



This video shows me at the opposite side again, but I move over to the preferred side, making my way through the kitchen. This can be a bad idea, but it is possible as demonstrated here:




EDIT: Trombonafide said this in the comments:

So using the Arcade Deathmatch method is definitely faster, even with a single controller.

Arcade Deathmatch
River
Lock all your teammates slots for a 1v5

Fill with Bots - ON
BOT difficulty - BEGINNER
Rounds to win: 10, but you can select higher with no affect, I usually do 20
Round score limit: 75
Execution Rules: OFF
Respawn time: 5 SECONDS
DBNO time: 1 seconds

Select Ben Carmine or Queen Myrrah. Get up to 7 skulls either by killing or dying and getting a second wind skull. Buy a boom shot and head to the Cafe or Town Hall building. Hide at the top of the stairs, but not in cover. When the enemies come up the stairs, boomshot them. Now dying enemies create a fire pool. They will endlessly run to their deaths. Keep an eye out in case an enemy gets by the fire. A round will last about 4 minutes, which equals out to 750 kills in 40 minutes or 1125 per hour. You can even squeeze in an extra kill or two at the end of every round if they enemies happen to be grouped together for a well placed boom shot.