As part of its effort to build out the AR-15 family of small arms, Colt introduced the Model 608 in 1965. This was intended to be an aircraft survival rifle, able to pack disassembled into a small space with four 20-round magazines for use by the US Air Force. With a 10 inch barrel, fixed tubular stock, and cut down grip it weighed just 4.75 pounds and had a maximum length of just 17.6 inches when disassembled. It was only produced as a prototype, with ten or fewer being made in total.

Many thanks to the Royal Armouries for allowing me to film and disassemble this rifle! The NFC collection there - perhaps the best military small arms collection in Western Europe - is available by appointment to researchers:
https://royalarmouries.org/research/national-firearms-centre/

You can browse the various Armouries collections online here:
https://royalarmouries.org/collection/