Hmmm, I think I felt a gentle bayonet poke in my ribs to contribute to this thread. Thanks US-Subs. I also had the opportunity to see that USMC display in the 90s but my photos didn't come out. It was the only time I've been let down by the trusty Nikon. Did you happen to get a shot of the entire display board? I recall there were some other interesting examples there.
Those are certainly three of the more interesting 40mm cartridges out there. The antenna round was developed for use with the AN/GRC-109 radio used by Special Forces and SEALs in Vietnam. As US-Subs mentioned, the projectile was supposed to penetrate the jungle canopy and string the green antenna wire out across the tree tops. The other end remained attached to the cartridge case remaining in the M79 launcher. The end would be cut off, stripped, and atatched to the radio for use.
These cartridges were made by AAI Corp. in Maryland on a limited, experimental basis. And according to an ex-AAI engineer I know who also owns one of the cutaway rounds, all of the wire was hand wound into the projectiles by a single employee there. I'm sure that was fun. Here are a few shots of the one I have.