Where Is The Serial Number On My Type II Derringer...?

[SteyrAUG]

I don't see one anyplace.

[DavidFagan]

I don't see one anyplace.

Under the barrel in front of the locking lug and under the left grip.
It however isn't necessarily a serial no but more likely a batch no depending on the exact variation. The only real value of this number is to know you have a original complete and not pieced together derringer.

[SteyrAUG]

Where would #417 approx. date my Derringer?

[DavidFagan]

Where would #417 approx. date my Derringer?

That's the $100 question, unless it's a short-line variation it's not a serial no it's a batch no, which repeated numerous times. Assuming a short-line (didn't repeat so it is a serial) 1888-1890, otherwise somewhere between 1891-1912. The serial no list has separations on variations which may close the gap with a picture of the top of your barrel but I wouldn't bet the farm on it but others may disagree and are certainly welcome to. I don't know off hand if Doug put this info in the new book or not.