50BMG is readily available. Google will show lots of hits.
20mm is another matter. This guy has some, but you need to be more specific
as to what type. The most common is the Vulcan cannon round, but other
vintage military weapons use Hispano, Oerlikon, Lahti and several other
types


Another source is
http://www.ows-ammunition.com/cgi-bi...42abca85&L=eng

They will have 50 BMG also

Randy


"Steve Mulhollan" wrote in message
...
I am looking for a small quantity of 50BMG and 20mm (and larger)
brass. If you have any, please contact me. Thanks.

Steve