The notching of the letters? Especially the T of UNITED...strong separation+notching. Is this your coin or one you found images of online?
I was checking the different classes of doubling on Wexler's site. the 64 d Jefferson nickel class 6. obviously you know...but so you know where I am looking. I swear I have found nickels that LOOK like this, but I would have passed them off for machine doubling.
If your is a 1964-D jefferson nickel, you cam also look if its a RPM ! heres a nice one I have, not sure if its a DDR or DDO, I haven't check, but I will today