Topic: NFEA Research Help - Land and groove impression measurements

[Blake Reta]

If you would like, please elaborate on your protocol for land and groove impression widths as critical measurements. Also, please provide what uncertainty (if any) you use when entering your measurements into the GRC database. EX: At the WVSP we will take the average of the measured land impression widths, and a +/- .005 variance to get our minimum and maximum land widths, the same is done for the groove impression widths. 
This information may be used in a research paper for the NFEA.

[Dwight Deskins]

Our system doesn't have a set variance we must follow.  I think this was intended to allow for typically damaged and distorted rifling measurements.
 
Our GRC protocol states "The GRC database is an investigative aid and should not be construed as an all-inclusive list of firearms available with those particular rifling characteristics.  The reported list of possible firearms may be as inclusive as needed based on case details and examiner discretion." 
 
So some analysts choose to use a search range of +/- 0.003" and others use +/- 0.005".  Some analysts may report only the most common firearms, while others report the entire list of possiblities returned.

[Lloyd Morse]

Our lab uses the .05 +/- variance, same as your lab.
 
 

[Steve Scott]

Get a rough average then search database with +/- 0.005"

[Blake Reta]

If those who voted in the poll and answered yes would not mind contacting me I would like to ask some additional questions.
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