Now, are slings actually worse than a grenade launcher or hand-thrown? A quick google search says that a sling has a range of 360-400m and a grenade launcher has an effective range of 350-400m, so about the same. As for issues about space and safety, watch this video https://youtu.be/yJ3bBkRIJNU. In particular, the overhanded technique and the two-handed technique look like they would be most applicable. They are fast, don't take up space next to you, and if the grenade is dropped accidentally it will only end up somewhere in front of the slinger and never behind them. They could potentially be done while the sligner is half obscured by the cover as well. Another benefit is versatility. 40mm grenades cannot be used as a hand grenade in a pinch, nor can most rifle grenades. However presumably a sling grenade could. Then troops would only have to carry one type of grenade that can be either used by hand at short distances or with a sling at long distances. Another obvious advantage is that slings are very quiet whereas grenade launchers are very loud. One of the major reasons why the US military switched to using 40mm grenade launchers instead of bazookas was because they were more discrete due to not having a backblast or a rocket trail leading back to the shooter. A sling doesn't even have muzzle flare. Also unlike a grenade launcher, a sling can be used to throw basically anything that would fit in the cup. Rocks, improvised grenades, hand grenades captured from the enemy, spy camera drones, etc. As for special sling grenades complicating logistics as they would be different than hand grenades, I don't see why you couldn't use a sling grenade by hand. A sling grenade would have to be egg shaped to be aerodynamic, it would need a pin, the clip might need to be deleted but not all grenades have one anyways. It's just a streamlined hand grenade and can be used as either. As it is 40mm grenades/rifle grenades are incompatible with the human hand and complicate logistics according to that logic. Sure, there are some use cases where the sling isn't as good as the alternatives, but there are also use-cases where the alternatives aren't as good as the sling. having a sling would just require tweaking of doctrine and tactics, just like any other new weapon system.