Someone was looking for info on the 6mm hazmat

Thought I would ask here

Fired captive-piston cartridges are considered "hazardous" to handle until the gas inside bleeds off and the pressure abates.

Maybe this is where the name came from?

Any single, captive piston round (silenced) needs to be registered NFA with the ATF as a silenced weapon if live.  

Found this from a silencertalk thread

Post by gixxerpilot750 » Thu Nov 24, 2016 1:02 pm

My understanding is that the firearm is not the restricted part of this equation, the ammunition is. In Paulson's Silencer History & Performance Vol 1 Arms Tech's 6mm Hazmat is mentioned on page 63. The same cartridge and the two barrel derringer type pistol chambered for it is pictured on pg 65 of Vol 2. The American Derringer Corp DA38 seems to have been the host firearm for the 6mm Hazmat. The Russian S4M or MSP (not sure which is the correct name, it's listed as both in the link below) looks really similar to a DoubleTap Defense two shot pistol, and given the fact the Doubletap has been chambered in 7.62x39 and 223, I'm sure it wouldn't be a stretch to have another set of barrels made. Otherwise take a look at American Derringer Corp's LM4, it looks almost identical to the SM4.