I just watched the episode of American Guns where they claimed to "build" a 20mm rifle - supposedly for avalanche control.
Several things about that "reality TV" episode did not make sense to me.
First off, they claimed that they started with a "surplus military action" - and brought in a rusted tube with an endcap on it.
What military 20mm used that thing as a reciever??!?
Next, they claimed the gun's owner - a private individual - would use "exploding war head ammunition" - but I don't think that ammo is available to any civilians, even if they could foot the $200 stamp required for every round.
On top of that, would 20mm even work for setting off avalanches? The buyer also grossly understated the range of current avalanche guns.
Finally, the gun they supposedly "built" at Gunsmoke looked suspiciouly identical to Anzio Iron's 20/50 rifle.
http://www.anzioironworks.com/Anzio-20-50.html
I'd like to believe that there is SOME truth in these shows - especially the gun-related ones. But, it looks like this reality show was complete BS when it comes to this gun, the "build" they supposedly did, and its origins.