Actually, the Dardick family is still trying to promote the design. They even received additional patents with the past few years.
The concept keeps popping up like a bad penny. I believe that the US Navy was playing with the .50 cal. Tround machinegun shown back in the late 1980s/early 1990s.
The USAF played with Tround Gatling guns during the 1960s. The TRW HIVAP could achieve a ridiculously high cyclic rate of ~30,000 rpm by virtue of its multiple feed positions and open chambers. Don Stoehr believed that by tweaking the feed, he'd be able to increase the rate of fire up to 42,000 rpm.