Yep, the US has one exactly like it, an MK-19 40 mm. Grenade Launcher. This is a direct competitor to it, like it says in the site
I've seen videos of the MK-19 being fired, you can probably put out a grenade every second...cover a mean area with that. BTW, I think they have fuses so that they have to go a certain distance before the fuse activates. 😀