Gears of War 4

The fastest way to get this would be with the assist of an engineer with ‘overclock’ skill on. Start from wave 14 on casual, that way you will be able to buy a weapons locker straight away and there will be a chance for drop shot Scions to be lurking around. Empty your boomshot and put it in the weapons locker until the ammo is full, rinse and repeat. With a max level heavy, you have 18 shots with the boom shot, so it will take less than 3 refills in the weapons locker.

To do this solo, the principle is the same, it would just take a little longer without the overclock skill.

Know Your Role: Heavy
You kept the damage coming with reloaded weapons from Weapons Lockers as a Heavy

For this achievement you will need to do the following: As a Heavy, add 50 ammo for launchers or Heavy Weapons in a Weapons Locker in one Horde match.
The fastest way to get this would be with the assist of an engineer with ‘overclock’ skill on.

This video will show you how to unlock the achievement + what cards you & the engineer should have on. I hope the guide helps, till next time stay frosty!!

This is possible solo and without any cards, and should only take about 10-15 min. Here's how:

Map: Dam
Mode: Juvey Madness
Wave: 14
Class: Heavy
Cards: preferably extra boomshot ammo, but you can do this without any cards.

Start by emptying your boomshot, then bringing the fabricator back to your spawn point, buy a weapons locker and place it a little bit farther back and stow your empty boomshot on it. Now let the juveys kill you.

Restart from current wave, once your weapon locker has fully reloaded your boomshot (full blue cog symbol), then shoot a single boomshot shot off into the distance (using the new boomshot that you respawned with), reload and pick up the boomshot from the weapons locker as amm,. Now simply shoot all your boomshot ammo away, place on the weapons locker again, and die while waiting for it to reload, rinse and repeat until the achievement unlocks.