FireFly SMG uses S&W M59 magazine
Originaly developed by Bob Irwin of Las Vegas Nevada. These guns do nothave a reputation for working well if at all. The porn star Marilyn Chambers and her then boyfriend Chuck Trainor at one time owned a pair of them. The second photo shows the serial number 069MC which is on the one formerly owned by Ms. Chambers.
Photo and information from: Mark H