Interesting about the Army cannon. I'm retired USAF and to me, Vulcan means a 20MM aircraft cannon. Gatling-gun style, six barrel, 6000 rds per minute. All US fighter aircraft have one. The A-10 air-to-ground attack aircraft uses a GAU-08 cannon, almost identical to the Vulcan but for 30MM rounds and fires just a tad slower.
I put 21 years into the USAF munitions community and had never heard of the Army version. That's an extremely BIG weapon to put on a ground vehicle.
The well known "mini-gun" used in choppers and by certain Terminators from the future is the same basic design but fires the smaller 7.62MM round.