The M203 underbarrel grenade launcher in Notoriety is used as an attachment for the M16/M4A1, and the game’s patch notes say it was added as the “M203 Launcher Underbarrel Attachment” for those weapons.

How to use it

  1. Equip an M16 or M4A1 with the M203 attachment.
  1. Treat it as a single-shot explosive launcher, so aim carefully rather than spraying.
  1. Reload after each shot, since it is not a rapid-fire weapon.
  1. Use it for grouped enemies, choke points, or targets behind cover where blast damage is useful.

Practical tips

  • The attachment is meant to complement the rifle, not replace it.
  • Save the launcher shot for high-value moments, because explosive ammo is limited.
  • If you are using the M16, the launcher changes the weapon’s role from pure burst-fire to burst-fire plus area damage.

Roblox context

There is also a lot of confusion online because “M203 in Roblox” can refer to different games, but for Notoriety the relevant reference is the underbarrel attachment added for M16/M4A1 in the 3.17.0 update. In other Roblox games, the M203 may behave differently or be obtained in different ways.

TL;DR

Use the M203 by attaching it to the M16 or M4A1, then fire it like a careful, single-shot explosive for clustered enemies and cover-breaking shots.