NOT-So-Small-Arms 30MM:

- Ever wondered why there's an official caliber limit for civilian owned 'Small-Arms' (US) set at .50" Caliber? (.50 inch is 12.7 millimeters)?

One explanation would be that 30.0mm equals 1.181 inches ..

GAU-8A 30 mm depleted uranium core ammunition is projected from GAU-8/A Avenger 'Gatling' style auto-cannon at up to 3,900 rounds per minute.

.. This I will concede - does somewhat relegate my sweetheart 'thirty-two' caliber into the mouse-gun zone.

Surely There Was Room To Slip-in a .32 ACP Cartridge On The Left.

"Why Don't Smiff & Western Make a Gun In 30 Millimeter?"

The A-10 Thunderbolt "WARTHOG" when firing it's full load of 30 mm ammo is slowed by 15 knots .. the recoil energy is actually greater than it's engines forward thrust - but the magazine is emptied rapidly.
 - AND the spent gasses from the cartridges - being inert & oxygen-free - can cause the aircraft's engines to 'flame-out'.😱

P.S. 

Hi Marty

There is no caliber limit in NZ.  If you have a Firearms Licence you may own and use (in the appropriate area) a firearm that meets ‘A category’ requirements regardless of bore size.  A 25 Pounder, 105mm howitzer, no problem!  They may only be used with solid shot though as the use of HE, smoke, etc. invokes a bunch of other legislation.

In the pre-1983 legislation, the Arms Act was limited to firearms of less than 20mm.  Anything over that was exempt from legal restriction.

Rod.

   Marty K.
After researching & writing 1,036 blogs I've got something NEW to try .. I've signed-up to Patreon. - In over five years I've not made one cent from this .. NOW you can send me a wee support $ - starting from $1. to get all this stuff from New Zealand - over a year that's nearly the price of one Shooting magazine. - Am I worth it?

https://www.patreon.com/user?u=16618870