The M60A1E4 was a conceptual variant that explored the use of a variety of remote managed weapons, which includes a 20mm gun as secondary armament. A mock-up of the style utilizing the Type C turret was built. The barrel latch system (a swinging lever) could capture to the gunner's devices https://hoytmachineguns.com/product/paws-inc-m-16-registered-receiver-with-extras/