I came across this a few years ago from the local gunshop ! there was a closing of a large military installation and a lot of stuff was just dumped into large dumpsters. A man found a box full of leather slings and holsters with this barrel. He took the box to the local gunshop and sold it outright, when they found the barrel they called me to see if I wanted it. They gave me the barrel.
Stoner 63/63A Automatic Rifle:
The Automatic Rifle is a closed-bolt rifle feeding ammunition from a top-mounted, 30-round magazine. The front and rear sights are offset to the left to compensate for the magazine's position. The AR does not have a semi-automatic mode. The automatic rifle configuration was field tested by the USMC for a short period during 1967.
Looks like a copy of the Bren Gun, probably done to influence potential British/Commonwealth buyers
Thanks for posting the photo of the Stoner 63A Automatic Rifle, my own opinion, if your going to carry a weapon this size, it is better to be belt fed. Both steel and aluminum 30 rd magazines were tested. I do not think that the "Bren Gun" configuration was done for any influence but rather as part of the package to show the different systems from a common receiver. I have a training manual for troops on the use of the Stone 63 rifle.
Before the Stoner 63 series, there was the Stoner 62 in 7,62mm NATO
The short barreled belt fed machinegun was in use by the US Navy SEALS into the 1970's,
I am sure they were reluctant to give them up.
Reed Knight was able to manufacture a small quantity of Stoner 63 weapons a few years ago. There is a service to convert the mechanism to use the common M27 link instead of the expensive and difficult to find Stoner S-63 link. The belt fed AR-15 can also be converted to use the M27 link too