I was digging around for information on my "HEP-NYC" 22 conversion unit. I have one very similar to yours. I too would like to find out more about it. The serial # on mine is 63. The difference in mine is that it has a 7.5 " barrel with two spacers for using it in alternate barrel lenghts. The barrel is marked "HEP-NYC" & "22LR" as well. It also has two lock nuts & a spring steel washer for the barrel installation. The threads on the barrel are some what of a bastard size. It is 3/8 -24 NF. but the major diameter is smaller than typical @ .3463" to fit down the 9mm tube. That's about all I know of it. If anyone else has something to ad, I would appreciate it.
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