I have Colt Overseas Sales Catalogs dated 1964 in three different languages. They show the M29 Rifle Grenade but European Version.
On my web page of Recoiling Launchers History I explain:
On the right is the European version of the Energa. Not visible is Mecar's Armaments and Munitions trademark. Unlike the Energas from US inventory which had rocket fins, the European version had a circular stabilizer. This particular practice projectile is dated 1962. While trying to sell its Model 01 version of the M16 to foreign countries, Colt's 1964 sales catalog advertised the rifle's compatibility with the Energa grenade. This projectile may have been a salesman's sample.
I do not remember the Colt picture having the depression in the front. This is a picture of a European one in my collection.
https://www.milsurps.com/images/impo...a_euro02-1.jpg