Introduced in 1968, the HK33 was Heckler & Koch’s adaptation of their roller-delay operating system to the 5.56mm / .223 Remington cartridge.
In addition to the standard full-length rifle (with a 15.35 inch barrel), a shorter version was made as the HK33K (with a collapsing stock and 12.4 inch barrel). HK also made a “submachine gun” variant, the HK53 (with an 8.3 inch barrel).
The HK33 tends to be overshadowed by its big brother the G3, and although it was not adopted by the Bundeswehr (or any other major European power), it did see use with German federal and state police forces, UK armed police, the SAS and SBS, Danish and German special forces, and also nearly became the new rifle of the French Army in the 1970s. It was also adopted by dozens of other countries, was licensed to Thailand which bought 40,000 rifles and bought the rights to manufacture 30,000 more. Malaysia also purchased 55,000 HK33s, and manufacturing rights were also sold to Portugal and Turkey – which has manufactured thousands of the rifle under license at the state-owned MKEK corporation. In the US the rifle was also popular in the 1970s and ’80s in its civilian form as the HK93.
The HK33 and 53 have always been one of my personal favorites, and in the video below, Ian from Forgotten Weapons gets up close and personal with a representative sample of the family.