The Long Bomb Penance/Achievement gives you a torso cosmetic for the Veteran and is necessary for the helmet cosmetic later on. This is a guide on how to throw grenades as Veteran so that you don’t need to yeet it across the map.
The Veteran Sharpshooter carries four krak grenades. There is a Penance/Achievement you need to complete called Long Bomb to get a torso cosmetic, as well as being a necessary achievement for a helmet cosmetic later on.
I found that most guides on this achievement point out specific parts of missions to do it on, but I was lazy so I figured out a more practical solution by quick throwing the grenade.
You’ll want to go to the Psykarium to practice throwing the grenades for a few minutes. Follow the hallway to the right when you spawn in the hub to find it.
With your grenades, stand about 20 meters away from a horde of weak enemies. Look up about 40 degrees or so (better to overthrow than underthrow) and just quickly left click without holding it.
This quick throw won’t go as far, and if done right, should explode a bit above head level.
Once you can do the throw comfortably, join a mission on the easiest difficulty (sedition).
Whenever you find a sizable horde, just let your teammates engage them while you stand back and do the throw. With a bit of luck and good practice, it shouldn’t take too long.
At trust level 10 for Veteran there is a feat that replenishes grenades every 45 seconds. With this feat you can attempt to throw multiple grenades at a horde, and if you don’t get it, you can always try again later in the mission.
Sometimes missions will have the condition “endless horde” which might make it easier to get the achievement.