I'd just like to say emphatically that I care about tracers and cannons!
Too bad I didn't take a picture of the 20mm I saw at the gunshow a week ago.  $22.6K and its yours, complete with two magazines the size of phone books each.  It was actually mounted on a bipod and shoulder fired!  The muzzle brake was near the size of my head, and it was about 7 feet long at least!
Benny, you ever even fired a weapon?