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Damaged Bullets

Home > Characterization and Evaluation of Fired Projectiles > General Riflling Characteristics > Damaged Bullets

In some cases, bullets bear no microscopic marks of value for comparison purposes because they are fragmented, distorted, deformed, or otherwise damaged.

There may be retrievable information if all of the following are present:

  • One or more measurable land impression
  • One or more measurable groove impression
  • Sufficient bullet remains to determine a measured caliber

Used with caution in selected cases, this information may allow a calculation of the number of land and groove impressions present prior to the damage.

If information exists to perform the calculation and if direction of twist can be determined, then sufficient information is available to search the GRC file for possible firearms that could have fired the bullet.

The formula for the calculation is as follows:  
Number of lands and grooves = multiply the estimated caliber by 'pi' and divide that product by LWD plus GWD

Applied to 9mm Luger bullet where:

  • Estimated caliber = 0.355 inches
  • Π = 3.1416
  • Land width dimension (LWD) = 0.069 inches
  • Groove width dimension (GWD) = 0.115 inches

 

Number of lands and grooves        = .355 * 3.1416 all divided by the sumation of .069 plus .115
                                                                               
                                                  = 1,115 divided by .184

                                                  = 6.06, or 6

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