The Maadi-Griffin MG-6 never made it to production.
(un-affiliated) Serbu Firearms, Inc. has a prototype semi-auto about to be tested (as of May 21, 2004)

Maadi-Griffin continues to sell sabot's and plan books as JNS Supply but no longer sells firearms.
We encourage those interested in purchasing an affordable, high-quality .50 cal BMG rifle or carbine to visit:
http://www.serbu.com/bfg50.htm

Serbu Firearms, Inc.
6001 Johns Road, Suite 144
Tampa, FL 33634

(813) 243-8899 (shop/fax)
mark@serbu.com