[MGunner]

Looks like someone turned a stock JG/TM on a lathe then put on O-ring on it.

I'm 99% sure that the PDI one is the same thing, accept its made from steel.

 

[MGunner]

Possibly.
How did you come across it?

 

[MGunner]

Hm.
It is wither an early production of the PDI one, or a one he turned on a lathe.