Gears of War 4

If you want to see the detailed stats on your progress with each weapon you can see it at a webpage I created:
http://24.216.206.219:8001/G4Maa

NOTE: If it isn't working or down for some reason, send me a msg on TA as I don't check this solution thread all that often.

FWIW, I've made a post in the site wishlist forum, asking about adding this functionality to TA for all multipart XB1 achievements. If you have a vote to spare, let them know you think this would be a useful feature for TA to add:
Track/Crowdsource Xbox One achievement sub-requirements

Update: It will also tell you which maps have the most weapons that you need. Thanks to Tom Live v7 for doing the work of compiling those in his solution.

Update 2: I’ve limited it to 1 check per 15 min so everyone can use it without it constantly running out. I’ve also been able to upgrade to the 400/hr package.

Update 3: just fixed bug that was making people with spaces in their tags show up as gamer tag not found.

Update 4: fixed it not working due to my password changing, also added in execution type tracking.

So now you don't have to screw around getting kills with a weapon just to see if you need them anymore.

As to the actual execution of it, Co-Op versus against casual bots is pretty easy. If you have a partner, they can down enemies with their lancer and you finish them off with the weapon of the moment. King of the Hill is one of the best modes for this as they will keep respawning and coming at the ring.

Also, weapon specific executions (long hold Y) do count towards that weapon, if you are out of ammo or something. And if you are not great with a weapon, down them with the lancer, then use the execution for the other weapon.

First off you can only earn progress towards this achievement in public matches and not private. Public matches do include the Versus AI playlists (any difficulty).

There are a total of 18 weapons in Gears of War 4 (not including grenades). Unfortunately heavy weapons do count so these will probably end up being the last weapons you will need to get 50 kills with.

Figuring out which weapons you have left to complete can be a bit difficult however you can initially use the war journal to get a partial idea under the ranked/social versus tab based on rifle kills, shotgun kills, pistol kills, etc. Unfortunately the Weapons tab mixes Campaign, Versus, and Horde weapon kills.

To get a better idea of the weapons you need you can use the achievement tracker. Use the overlay during gameplay and get 1-3 kills with a particular weapon. This should show partial progress (not always +1%) if you haven’t already got 50 kills with that weapon (you should see the tracker bar highlight slightly).

To start you can get the 5 loadout weapons complete easily by jumping in any game and focusing on them. To follow you can either use the Arms Race gametype or view the map list below to determine where best to find the other weapons you choose to go for.

Loadout Weapons: Lancer, Gnasher, Snub, Hammerburst, Enforcer

UPDATE - Hammerburst is no longer a loadout weapon. Use this link to find the maps it will now be placed on:
https://gearsofwar.com/en-us/community/whatsup-mar1-2018

Secondary Weapons:

Boltok
Avalanche, Blood Drive, Canals, Checkout, Clocktower, Dam, Dawn, Drydock, Forge, Forge Blitz, Fuel Depot, Glory, Gridlock, Harbor, Hotel, Impact Dark, Lift, Lift Apex, Mercy, Old Town, Reclaimed, Reclaimed Windflare, Security, The Slab,

Markza Mk. 1
Dawn, Fallout, Forge Blitz, Harbor Haze, Old Town, Relic, Security,

Retro Lancer
Checkout, Dam, Diner, Forge, Fuel Depot, Reclaimed, Reclaimed Windflare, Security,

Overkill
Avalanche, Forge, Impact Dark, Lift, Old Town, Security,

Power Weapons:

Boomshot
Clocktower, Dam, Forge, Forge Blitz, Foundation, Fuel Depot, Gridlock, Glory, Harbor Haze (after fog), Hotel, Lift, Lift Apex, Old Town, The Slab,

Dropshot
Avalanche (after avalanche), Clocktower, Dam, Dawn, Fallout, Forge Blitz, Foundation, Glory, Harbor, Hotel, Impact Dark, Lift, Lift Apex, Old Town, The Slab,

EMBAR
Checkout, Dam, Diner, Fallout, Harbor, Hotel, Lift Apex, Reclaimed, Reclaimed Windflare, Relic,

Longshot
Avalanche, Blood Drive, Canals, Checkout, Clocktower, Dam, Diner, Drydock, Forge Blitz, Fuel Depot, Gridlock, Harbor, Impact, Lift, Lift Apex, Old Town, Reclaimed, Reclaimed Windflare, Speyer, War Machine,

Torque Bow
Avalanche (after avalanche), Blood Drive, Canals, Dawn, Drydock, Fallout, Forge, Forge Blitz, Foundation, Harbor Haze, Hotel, Impact, Mercy, Old Town, Relic, War Machine,

Heavy Weapons:

Trishot
Avalanche, Drydock, Lift, Mercy, Reclaimed, Reclaimed Windflare, Rustlung, Security,

RL-4 Salvo
Rustlung (after approx. 5 minutes), Speyer,

Buzzkill
Avalanche, Blood Drive, Impact, Reclaimed, Reclaimed Windflare, Relic, Security,

Mulcher
Checkout, Impact, Mercy, Relic,


Notes:
- Raven Down has no weapons towards this achievement.
- Some weapons cycle between rounds.