Wirnsberger,s book, The Standard Directory of Proof Marks, is available as a reprint from Gunnerman Books. Price is $35.Tel; 248-608-2856.
The Gun Digest Treasury, Published in 1960 contains a series of articles on European and British proof marks that is second to none!The articles covers 72 pages it includes many illustrations. The author is A.Baron Englehart.A hard to find book, but it is truly a treasure.
The Shooting Sportsman,Jan-Feb 2009 contains an excellent update on the British rules of proof.Author is Vic Venter,one of several superb articles published, by Vic,under the heading, "Guncraft".
