https://www.rockislandauction.com/detail/71/1539/hr-reising-prototype-7-62-rifle-full-transferrable-machine-gun

In the late 1950s or early 1960s, Eugene Reising experimented with adapting the mechanism of his submachine guns to a locked-breech 7.62mm NATO military pattern rifle. The resulting rifle used an M14 gas piston and a bolt that was fully locked into the top of the receiver (instead of being a delayed blowback like the SMGs). It was assembled into the stock from an H&R .22 caliber M!4 simulator, which was another rifle also designed by Reising.

Ultimately the design was not successful, although I have no specific data on why.

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