It is an original and extremely rare 4.92mm caseless round designed for the HK ACR series of rifles by Heckler and Koch. This is one of the later iterations where the propellant is a HITP nitrocellulose block (hence why it’s an orange brick shape) complete with a disintegrating primer, a 4.92mm slug, and a plastic cap. I’ve had this round in my possession for about three years now and I am planning on donating it to the National Infantry Museum in Columbus, Georgia (they do have a G11 ACR prototype in their possession)

Notice how I said HK ACR instead of “G11”, that is because they fired different ammunition from each other. The G11 fires a 4.73×33mm caseless round, but HK decided to scale up the cartridge for specifically the ACR program series of G11s, hence, leading to the 4.92x34mm caseless round