What are the limits on a destructive device?

[Lawmaker]

You can find tanks for sale. Some of the main guns work.
http://armyjeeps.net/armor1.htm
http://www.tanksforsale.co.uk/Tanks_Trucks_Jeeps_for_sale_page.html

 

[kilimanjaro]

I kind of want a 36-gun frigate and Letters of Marque, should have no trouble getting a crew...

 

[JL Wesson]

I wuold like to shoot a mortar. Anything that fit in the trunk of my car will do: may be not on the huge side but it looks fun to me the "indirect shooting".

The 36-gun frigate idea from Kilimanjaro is also intriguing a lot!!! 12 pounds guns I suppose...
the real deal is the letter of marque: you can do a lot of good with that!