At last an excellent book on gunshot residues. In Europe Dr. Wallace is very well known in the forensic family interested in GSR (by the way, in the UK they are called FDR, Firearms Discharge Residues) for his researches on the subject, on ammunition and on primers chemical composition. I have met him several times in Belfast, at the NIFS Laboratory, and I was constantly impressed by his work and by his encyclopaedic knowledge of the topic.
His book apparently was written in two different periods and probably the first part was ready in the early nineteen's and, later, the Particle Classification Scheme has been updated: we cannot but agree with him when, at page 272, the author affirms that "No longer can a 'unique' FDR particle be described as such as they occur from nonfirearms sources."
Two personal remarks. I feel the absence of a paragraph describing the formation of GSP and the absence of a general bibliography.
In my opinion it is an highly recommended book for forensic scientists seriously working on Gunshot Residues.