- 01: Introduction
- 02: History
- 03: Propellants, Firearms, and Ammunition Development
- 04: Modern Firearms Manufacture
- 05: Small Arms Ammunition
- 06: Evidence Handling Procedures
- 07: Equipment and Instrumentation
- 08: Examination of Firearms
- 09: Cartridge and Shotshell Examination
- 10: Characterization and Evaluation of Fired Projectiles
- 11: Bullet Comparison and Identification
- 12: Gunshot Residue and Distance Determination
- 13: Toolmark Identification
- 14: Communicating Results
- Resources
Comparison Process
Home > Bullet Comparison and Identification > Microscopic Procedures > Recovered Firearm Without Related Evidence > Comparison Process
The comparison of test bullets should be performed according to laboratory protocol.
Click here to watch a bullet comparison demonstration
A sample procedure follows:
- Recover test fired bullets from the submitted firearm.
- Mark the test bullets and indicate the sequence in which they were recovered.
- Use a stereomicroscope to determine the presence and quality of microscopic marks on the test bullets prior to examination under the comparison microscope.
- Place one of the test fired bullets on the right stage of the comparison microscope. Attach the nose of the bullet to the mount.
- Adjust the lighting from the rear of the microscope to provide oblique illumination over the bearing surface of the bullet.
- Examine the entire bearing surface of the test bullet using low magnification (10x-20x) to determine the best area of individual characteristics. When such an area is located, leave the right stage in that position.
- Place a second test bullet on the left stage with the nose in the same direction as the bullet on the right stage.
- Rotate the bullet on the left stage looking for the same area of individual characteristics as on the bullet on the right stage. The entire surface of the bullet should be considered. Higher magnifications should be used to verify the correspondence of finer striations.
- If an area of correspondence is found, align the land or groove impressions and rotate both bullets simultaneously. Examine and compare each land impression and each groove impression area from base to nose until it a conclusion can be drawn that there is or is not sufficient agreement for identification.
Note that:
- These examinations should be made with the bullets in phase. This means that the edges of the land and groove impressions of both bullets align with each other and the relationship of the other land and groove impressions in the viewing area is the same.
- Agreement is sufficient when it exceeds the best level of agreement demonstrated between bullet striations known to have been produced by different barrels (the best known nonmatch).
| Note: |
| During training, firearm examiners must compare test fired bullets to bullets fired through a series of barrels of the same make and model. This serves to inform the student of the striation mark agreement necessary to constitute an identification and to distinguish this from bullets with similar striation marks known to have been fired through different barrels. |
- If an identification cannot be made between the test bullets (there is not sufficient agreement), then more test bullets should be fired and compared. If an identification still cannot be made, the examiner may reach the conclusion that the barrel of the firearm in question does not consistently produce sufficient individual marks to warrant an identification.
- If an identification can be made, the area of best agreement or the area with the most obvious striations should be indexed with a permanent marker at the base and nose for later use in comparisons with evidence bullets. Indexing allows an examiner to quickly return to an area of correspondence.
