I was referring to the storage compartment in the tang of the Mod. 17. On page 178 of Bob Gaddis' book you can see it. (The catalog calls it a slot.)

It remains a clever idea but not terribly practical in the 21st century.
_________________________
David Longenecker
R.K.C.C. #CM83
RKS#1691
N.R.A. Endowment Life Member
Residing somewhere in the Ubiquitous States of Amnesia