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ЛОГОТИП СГУ

 

Trace and mark examination features on deformed
bullets in firearm identification

 


Vladimir А. Fedorenko

Saratov State University,
Laboratory Microanalysis and Modeling
of the Weapons Results Application
E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Yuri V. Iliasov

SBC Co.Ltd.

Aim: development of the algorithm of the firearm identification in the striation pattern on the deformed bullets with ballistic identification systems

1. The Definition of the Type Strain of the Bullet
Basic types of deformations of the bullet
                      


Fig. 1., Type 1

Fig. 2., Type 2

Fig. 3., Type 3

Fig. 4., Type 4

 

                                                                                
Fig. 1. Bullets with deformation that resulted in a little change of bearing surface proportions have the 1 type of the deformation.
Fig. 2. Bullets have second type of the deformation, if the bearing surface diameters expended evenly along the full length.
Fig. 3. An uneven expansion of bullet diameter at a particular part of a bullet (the interval of [a-b], Fig. 3) may be referred to the third type of deformation.
Fig. 4. Uneven change of the bearing surface area along the full length may be comprised to the forth type of deformation

2. Firearms Identification by Traces on Bullets, Having Elliptic Shape at Cross-Section (First Type Deformation)


Fig. 5.

Fig. 6.

Fig. 7.


Fig. 5. The coefficient of the bullet ellipticity at cross-section K=a/b.
Fig. 6. Distortion of the tool mark is caused by the curvature of the bullet: 1 – Typical distortion of the undeformed bullet; 2 – Minor additional distortions caused with increasing curvature of the deformed bullet at К<2.5; 3 – Significant distortions caused with the increase of curvature of the deformed bullet at К<2.5-3; 4 – The distortions caused by the slope of the scanned surface to the plane of the CCD.
Fig. 7. The areas with minor curvature radius need mark on the digital images of bullet evolvents (angle intervals [a-b], [c-d])

Traces can be considered suitable for a comparative study with ballistic identification systems and for making a search in the digital bullet database at K < 2.5 and width of the recording frame no more than 0.6 mm.


Recomendations:

  • To assess ellipticity bullets in cross-section. At  K> 2.5 should refuse scan study bullets;
  • At К < 2.5, the scanning of  bullets can be carried out.  Area with a small radius of the curvature are recommended to mark on the digital bullet evolvents

3. Firearms Identification by Traces on Bullets, Having Slightly Different Diameters (Second Type of the Deformation)

  (2)
Table № 1 Gives maximum permissible values of the    deformation ∆εmax of one bullet relative to the other with   striation  width of 20-35 microns.

Caliber, mm

Δεmax

Caliber, mm

Δεmax

5.45;  5.6

0.044

9.0;  9.2

0.027

7.62; 7.63;7.65

0.032

11.43

0.021

 

Fig. 8. Divergence overlapping of secondary trace striations depending on the difference between the diameters (ΔD) of the study bullets.

That is why this tool marks can be admitted as partially permissible for the search through the bullet database

Recommendations:
  • To assess the deformation of the bullet relatively to the experimental study of bullets (Δε);
  • At Δε < Δεmax, tool marks can be admitted as  permissible for the searchthrough the bullet database and firearm identification;
  • At Δε > Δεmax, tool marks can be admitted as partially permissible for the searchthrough the bullet database and firearm identification.

 4. Firearm Identification at Tool Marks on Fired Bullets, Having Third Type of the Deformation


For the scanning it can be recommended to use the marks on those areas of bullet bearing surface where deformation agrees with the first or the second types of deformation (interval [b-c], Fig. 3)

Recommendations:

  • the investigated bullets to scan only on the interval [b-c] (Fig. 3);
  • To store the general form of digital images of the deformed bullets in the bullet datebase.

 

5. Firearm Identification at Tool Marks on Fired Bullets, Having Fourth Type of the Deformation

   Tool marks on bullets №2 and №3 are not permissible for comparative study; Tool marks on bullets №1 partially permissible for the firearms identification (Fig. 4). In the study of bullet №1 two possible situations.



1-st situation
We will compare the marks on a bullet with a conical shape of the bearing surface and the marks on a cylindrical bullet (Fig. 9).

 

      Dmax/min = A(1± Δεmax)       (3)
Fig. 9.

Recommendations:

  • To determine the height h where the diameter of the first bullet equal to the diameter of the second one (D=A);
  • To determine a width of the evolvent bend (S) for the first bullet (Fig. 9), ensuring the correctness of the comparison of tool marks and the correctness of the search in electronic bullet databases;
  • For comparison examination it is necessary to use only those marks on the first bullet that are located in the limits of the marked bend.
    • To determine a widths of the evolvent bends (S) for each bullet, using a measuring equipment and formulas (4), (5);
    • Bullets to scan in accordance with the selected areas of the recording;
    • It is necessary to compare the bends with the same sequence numbers.
    • The conicity of the bearing surfaces of compared bullets should not differ a lot. Otherwise the last bends with the same sequence numbers will have a fundamental difference of the heights of their location.
    • The conicity of the bearing surfaces of compared bullets should not be large. Otherwise the quantity of bends will increase.
    • Tool marks on bullets, having large conicity of the bearing surfaces are considered to be unuseful for the comparative research and, accordingly, to the search throught the bullet database.
  •  

    2-nd situation
    Two bullets were submitted for the examination. The bearing surfaces of these bullets have a conical shape as a result of deformation (Fig.10)


    Fig. 10
    DN(max)=A(1+Δεmax)N        (4)    
    DN(min) = A(1+ Δεmax)N-1   (5) 
    N – is a bend sequence number

    Recommendations::

     

    Limitation:

    The example of the correct scanning of the deformed bullets for the comparison of the tool mark (Fig. 11, 12)


    Fig.11

    Fig. 12.

     

 

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