I remember a "behind the scenes" or a "making of" special on the X-Files, and they mentioned that prop.
I can't recall much about the piece, but I do remember them mentioning that the blade is longer than the handle.
I think it was manually opened as well, instead of pneumatic pressure. Not 100% on that though.
I went the cheap route and modded out a nail punch with an ice pick to make the one I had :lol