Congruent Matching Profile Segments 

(CMPS) Method for Objective Comparison 

of Deformed Bullets

Zhe Chen, John Song, Johannes A. Soons, Wei Chu

Forensic Topography and Surface Metrology Project

Sensor Science Division (Div. 685), PML, NIST

Robert M. Thompson, SPO, NIST

Forensics@NIST, November 7-8, 2018

National Institute of Standards and Technology

Gaithersburg, MD 20899, USA
Funding was provided by the 

Special Programs Office (SPO) of 

the National Institute of Standards 

and Technology.

2

Acknowledgements:
Disclaimer

Certain commercial equipment, instruments, or 

materials are identified in order to specify the 

experimental procedure adequately. Such 

identification is not intended to imply 

recommendation or endorsement by NIST, nor is 

it intended to imply that the materials or 

equipment identified are necessarily the best 

available for the purpose. 

3
1. Motivation

2. Overview -- samples, measurements and filter 

process

3. Challenges to correlations of deformed bullets

4. Profile/image re-construction process

5. CMPS method

6. Correlation results for deformed reference bullets

7. Correlation results for pristine reference bullets

8. Correlation results for different bullet jackets 

9. Discussion and future work

Outline:

4
• For research of bullet identifications, the 

bullet samples used in validation tests are 

often pristine.

• However, the bullets found at a crime 

scene are often deformed or fragmented.

• Firearm examiners face additional 

challenges when comparing these 

samples. 

• This study addresses the comparison of 

deformed bullets.

Motivation

5

By Courtesy of Ultra Electronics 

Forensic Technology, Inc.
• 57 bullets of 7 ammo brands (in 7 bags) were received.

• All bullets were fired from the same 9 mm Luger pistol.

With different types of ammo brands, this test considers:

1. bullet design.

2. bullet jacket material, even with the same kind of 

metal (like copper), the hardness or other 

characteristics of the jacket between different ammo 

brands can be different.

3. firing performance, mainly affected by the types and 

quantities of gunpowder.

Overview of the samples

6
Bag 1: 6 Remington UMC (copper) Bag 2: 8 PMC Starfire (copper)

Bag 3: 7 Speer Gold Dot (copper) Bag 4: 8 Hornady (copper)

Overview of the samples

7
8

(continued)

Bag 5: 9 Federal Premium (copper) Bag 6: 9 Federal Classic (copper)

Brass is an alloy of copper

and zinc, which is harder

than pure copper. The color

is also different with copper. 

Bag 7: 10 Remington Golden Saber (brass)

8
The bullets were measured using a confocal microscope. For 

each measurement day, the measurement procedures were:

1. Mirror calibration to create a reference for the microscope.

2. Check SRM 2073, sinusoid,

λλcc = 0.8 mm, RRaa = 3.054 ± 0.038 μm.

3. Check SRM 2460 standard bullet 

land engraved area (LEA) #1.

3. Measure bullet samples.

4. Re-check using the two specimens in step 2 and 3.

Overview of measurements

9
Metal jacket 

adheres to the 

lead core. Nose 

area expanded 

due to impact.

Use pliers to bend 

the nose. Be careful 

to avoid contact with 

the base, keep the 

LEAs on the base 

untouched.

Put the sample on 

the holder. 

Sometimes wax is 

needed on the 

nose area for 

fixture.

Measurement of relatively intact samples

Overview of measurements

10
We used a 20X objective (NA 0.6). The pixel separation distance 

was 0.68 μm

Measurement of deformed and fragmented samples

Metal jacket is detached

from the lead core. Pliers 

were used to bend the 

jacket to make it 

measurable.

Hold the sample by wax, 

then wait until the wax fully 

solidifies. It took about 4~5 

minutes for the 

solidification process.

(continued)

11
• Some outliers, dropouts, and all shoulders of the 

topography images were removed manually. The 

pixel spacing was then decreased to 1.35 μm.

• A 2nd-order Gaussian regression high pass filter was 

applied with a cut-off length λc = 250 μm.

Image pre-processing

Original topography Filtered topography Remove shoulders and 

decrease pixel spacing

12

0 500 1000 1500 2000 2500 3000

Pixel

0

500

1000

Pixel

57.34

100

200

300

362.61

μm

0 200 400 600 800 1000 1200 1400

Pixel

0

100

200

300

400

Pixel

71.04

150

225

300

317.22

μm

0 200 400 600 800 1000 1200 1400

Pixel

0

100

200

300

400

Pixel

-22.05

-10.72

-7.5

0

7.5

10.14

21.83

μm
Challenge to correlation of deformed bullets

When fired bullets hit a solid surface like a wall or decelerate

in a body or water tank, the nose of the bullet may expand. 

0 200

Pixel

0

200

400

600

800

1000

1200

1400

Pixel

-12.94

-4.25

-2.5

0

2.5

3.84

24.16

m

Base area of the bullet land 

engraved area (LEA) is 

without or with minor 

deformation, which can be 

used as a reference for the 

image re-construction.

Towards the nose area of the 

bullet, the LEA is expanded. 

The LEA expansion is higher

near the shoulders, and 

smaller at the central part.

Optical image Filtered topography

13
The left bullet is expanded, which makes it difficult to 

match the whole land engraved area (LEA) with the right 

reference bullet.

Deformed bullet comparison using a 

comparison microscope

Upper 

part 

matched

Lower 

part 

matched

14
Profile/image re-construction

c. Align the profiles of the base part to 

create a reference for the segment.

a. Divide the LEA image horizontally into 

segments.

b. For each segment, find the base part 

with least deformation.

15
(continued)

f. Stitch the re-constructed segment 

images together.

e. Re-construct the segment image by 

moving and scaling each of the 

remaining profile sections to match 

the base reference.

16
Image processing (obtain LEA profile)

a.

b.

d.

e.

f.

1 2 3 n

c.

a. Filtered image after 

confocal image 

preprocessing

b. Striation edge 

detection

c. Mask image

d. Image with invalid 

area removed

e. Test twist angle θ

f. The compressed 

signature profiles 

are divided into 

profile segments for 

correlation

17
Complete profile correlation

0 200 400 600 800 1000 1200 1400 1600

Pixel

-20

0

20

μm

reference profile

comparison profile

The maximum overall similarity value (using normalized CCF) 

between the reference and comparison profiles is only 0.43.

shows the matching parts between the profiles

shows profile misalignment due to lateral deformation 

18
19

Congruent Matching Profile Segments (CMPS) μm

• Divide the reference 

profile into 

segments.

• For each segment, 

obtain a similarity 

curve by moving the 

segment along the 

comparison profile.

• The similarity curve 

describes the profile 

similarity (CCF) as a 

function of the 

registration position.
CMPS method (multi-segments correlation)

20

Similarity: The similarity curve of each segment is summarized by the 

sample positions of three highest similarity peaks.

Congruency: At the true matching position, most segments should 

have a similarity peak at approximately the same sample position.
The CMPS number is the maximum number of profile segments 

that have a similarity peak at the “same” position.

In our test, the segment length is 50 pixels (67.7 μm) and the 

tolerance zone for a congruent position is 12 pixels (16.25 μm).

(continued)

21
Consequences of incomplete samples

LEA GEA Missing LEA

Some LEAs in a bullet are not available for measurement. 

This can cause a false negative result.

Possible reference LEA

Land engraved areas in Reference bullet

Land engraved areas in Comparison bullet

22
A3 is the reference LEA. Suppose LEA B5 is missing. The 

maximum correlation score between LEA A3 and bullet B is 

now 3, instead of 8.

In this study, the maximum CMPS score of all LEA to LEA 

comparisons is reported for each bullet comparison.

Consequences of incomplete samples

23
0

200

400

-36.12

-16.86

-10

0

10

15.55

36.11

μm

0 200 400 600 800 1000 1200 1400

Pixel

0

200

400

Pixel

-40.66

-15.61

-10

0

10

14.41

39.38

μm

0 5 10 15 20

CMPS number

0

0.05

0.1

0.15

0.2

0.25

Frequency

Original (56)

Re-construction (56)

Correlation results of deformed bullets

The re-construction of bag 2 (PMC Starfire) bullet 5 LEA 6

• 15 LEAs (out of 250 in total) showed major deformation.

• 10 of the 15 deformed LEAs show improved CMPS results after 

the profile re-construction process. Subjectively, samples with 

relatively large deformations and good image quality tend to 

have better improved CMPS results after profile re-construction.

24
0 5 10 15 20 25

CMPS number

0

0.05

0.1

0.15

0.2

0.25

Frequency

Original (56)

Re-construction (56)

The re-construction of bag 7(Remington Golden Saber) 

bullet 7 LEA 6

• 5 of the 15 deformed bullet LEAs showed little change in CMPS 

distributions after the profile re-construction process.

• For samples with approximately parallel striae, the CMPS 

method can, by itself, correct local scale differences.

0

200

400

-11.658

-7.272

-4

0

4

7.37

15.692

μm

0 200 400 600 800 1000 1200

Pixel

0

200

400

Pixel

-11.777

-7.131

-4

0

4

7.23

15.977

μm

Correlation results of deformed bullets

25
2 bullets with 6 intact lands were selected as references:

Each bullet is correlated with the other 56 bullets. 

Bag 4 (Hornady) 

Bul. 3 

Correlation results using reference bullets

Bag 4 (Hornady) 

Bul. 4 

CMPS result using reference Bag 4 bullet 3

 1 1 1 1 1

 5

 7

 5

 7

 6

 7

 12

 2

0 5 10 15 20 25

CMPS number

0

0.05

0.1

0.15

0.2

0.25

Frequency

CMPS result using reference Bag 4 Bullet 4

 1 1 1 1 1 1

 3

 2

 3

 10

 7

 9

 11

 5

0 5 10 15 20 25

CMPS number

0

0.05

0.1

0.15

0.2

0.25

Frequency

CMPS = 6 CMPS = 6

26
The two false negative CMPS results

1) Bag 6 (Federal Classic) bullet 5 

Pacakge6 bullet5 land1

0 500

Pixel

0

200

400

600

800

1000

1200

Pixel

-12.88

-5.25

-3

0

3

5.7

19.27

Package6 bullet5 land2

0 200 400

Pixel

0

200

400

600

800

1000

1200

Pixel

-26.97

-8.25

-5

0

5

8.56

26.96

Package6 bullet5 land3

0 500

Pixel

0

200

400

600

800

1000

1200

Pixel

-34.78

-11

-7.5

0

7.5

10.27

34.76

Package6 bullet5 land4

0 200 400

Pixel

0

200

400

600

800

1000

1200

Pixel

-29.31

-8.78

-5

0

5

8.21

29.25

There are 4 LEAs available for measurement in bullet 5. 

the CMPS results with the 2 reference bullets are both 4. 

27
2) Bag 6 (Federal Classic) bullet 7

There is only 1 LEA available for measurement in bullet 7. the 

correlation results with the 2 reference bullets are both 0. 

Main reason for the false negative results is the bad quality of 

the bullet 7 sample topography.

Package6 bullet7 land1

0 200 400

Pixel

0

200

400

600

800

1000

1200

Pixel

-13.07

-5.8

-4

0

4

6.5

20.59

The two false negative CMPS results

28
Correlation results using different jackets

Reference: Bag 4 (Hornady) bullet 3 (copper jacket)

Copper jacket (46 correlations) Brass jacket (10 correlations)

Package 7 (Remington 

Golden Saber) Bullet 9

Package 6 (Federal 

Classic) Bullet 1

0 5 10 15 20 25

CMPS number

0

0.05

0.1

0.15

0.2

0.25

Frequency

Copper jacket (46)

Brass jacket (10)

Brass and copper have 

different hardness and 

color, but there is no 

obvious difference 

between their CMPS 

scores.

29
Discussion

• We observed 15 LEAs (out of 250 in 57 bullets) with 

major deformation.

• 10 out of the 15 deformed bullet LEAs showed 

improved CMPS results after profile re-construction. 

Subjectively, profile re-construction seems to work 

best for samples with relatively large deformations 

and good image quality.

• 5 out of the 15 deformed bullet LEAs don’t have a 

significant change in CMPS distributions after 

profile re-construction. For samples with 

approximately parallel striae, the CMPS method 

can, by itself, correct local scale differences.

30
• The false negative results mainly

occurred for samples with poor quality 

striation patterns.

Future work

• Effects of image re-construction on comparison 

scores of known non-matching (KNM) samples

31

Discussion Package6 bullet5 land4

0 200 400

Pixel

0

200

400

600

800

1000

1200

Pixel

-29.31

-8.78

-5

0

5

8.21

29.25

• Comparisons involving different jacket 

materials (copper with copper vs. 

copper with brass) didn’t show an 

obvious difference in their distributions. 
Thank You

Contact: zhe.chen@nist.gov
Appendix (10 improved LEA results)

33

0

200

400

-36.12

-16.86

-10

0

10

15.55

36.11

μm

0 200 400 600 800 1000 1200 1400

Pixel

0

200

400

Pixel

-40.66

-15.61

-10

0

10

14.41

39.38

μm

0 5 10 15 20

CMPS number

0

0.05

0.1

0.15

0.2

0.25

Frequency

Original (56)

Re-construction (56)

The re-construction of bag 2 bullet 5 land 6

0 200 400 600 800 1000 1200 1400

0

200

400

-22.05

-10.29

-7.5

0

7.5

9.91

21.65

μm

0 200 400 600 800 1000 1200 1400

Pixel

0

200

400

Pixel

-22.87

-7.6

-4

0

4

7.57

22.25

μm

The re-construction of bag 2 bullet 7 land 3

0 5 10 15 20 25

CMPS number

0

0.05

0.1

0.15

0.2

0.25

0.3

Frequency

Original (56)

Re-construction (56)
34

The re-construction of bag 2 bullet 8 land 3

10 improved LEA results

0 5 10 15 20 25

CMPS number

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Frequency

Original (56)

Re-construction (56)

0

200

400

-13.91

-8.72

-5

0

5

8.56

18.35

μm

0 200 400 600 800 1000 1200 1400

Pixel

0

200

400

Pixel

-12.93

-8.07

-5

0

5

7.92

20.28

μm

The re-construction of bag 4 bullet 7 land 2

0 5 10 15 20 25

CMPS number

0

0.05

0.1

0.15

0.2

0.25

0.3

Frequency

Original (56)

Re-construction (56)

0

100

200

-12.94

-8.31

-5

0

5

7.84

24.14

μm

0 200 400 600 800 1000 1200 1400

Pixel

0

100

200

Pixel

-12.94

-8.11

-5

0

5

7.64

24.6

μm
35

The re-construction of bag 6 bullet 2 land 1

10 improved LEA results

The re-construction of bag 6 bullet 3 land 3

0

200

400

-17.91

-11.38

-7.5

0

7.5

11.08

22.21

μm

0 200 400 600 800 1000 1200 1400

Pixel

0

200

400

Pixel

-16.89

-11.18

-7.5

0

7.5

10.88

23.44

μm

0 5 10 15 20 25

CMPS number

0

0.05

0.1

0.15

0.2

0.25

Frequency

Original (56)

Re-construction (56)

0 5 10 15 20 25

CMPS number

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Frequency

Original (56)

Re-construction (56)

0

200

400

-13.766

-7.124

-4

0

4

7.371

14.63

μm

0 200 400 600 800 1000 1200 1400

Pixel

0

200

Pixel

400

-13.766

-6.133

-4

0

4

6.296

14.772

μm
36

The re-construction of bag 6 bullet 4 land 2

10 improved LEA results

The re-construction of bag 6 bullet 6 land 1

0

100

200

300

400

-11.748

-8.606

-5

0

5

8.684

17.613

μm

0 200 400 600 800 1000 1200

Pixel

0

100

200

300

400

Pixel

-11.759

-8.49

-5

0

5

8.564

17.613

μm

0

200

400

-13.28

-9.88

-7.5

0

7.5

10.42

24.62

μm

0 200 400 600 800 1000 1200 1400

Pixel

0

200

400

Pixel

-13.81

-9.66

-7.5

0

7.5

10.09

25.64

μm

0 5 10 15 20 25

CMPS number

0

0.05

0.1

0.15

0.2

Frequency

Original (56)

Re-construction (56)

0 5 10 15 20 25

CMPS number

0

0.05

0.1

0.15

0.2

0.25

Frequency

Original (56)

Re-construction (56)
37

The re-construction of bag 7 bullet 6 land 1

10 improved LEA results

The re-construction of bag 7 bullet 7 land 5

0

100

200

300

400

-13.65

-9.2

-5

0

5

9.1

18.62

μm

0 200 400 600 800 1000 1200

Pixel

0

100

200

300

400

Pixel

-13.61

-8.06

-5

0

5

8.02

19.64

μm

0

100

200

-10.128

-7.051

-4

0

4

6.91

14.192

μm

0 200 400 600 800 1000 1200 1400

Pixel

0

100

200

Pixel

-10.421

-6.3

-4

0

4

6.123

14.192

μm

0 5 10 15 20 25

CMPS number

0

0.05

0.1

0.15

0.2

Frequency

Original (56)

Re-construction (56)

0 5 10 15 20 25

CMPS number

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Frequency

Original (56)

Re-construction (56)
38

The re-construction of bag 1 bullet 3 land 3

5 little changed LEA results

The re-construction of bag 2 bullet 8 land 1

0

100

200

300

-26.67

-13.72

-7.5

0

7.5

13.05

22.19

μm

0 200 400 600 800 1000 1200

Pixel

0

100

200

300

Pixel

-26.13

-13.62

-7.5

0

7.5

12.95

21.03

μm

0

200

-35.22

-12.69

-7.5

0

7.5

12.46

47.04

μm

0 200 400 600 800 1000 1200 1400

Pixel

0

200

Pixel

-35.87

-12.07

-7.5

0

7.5

11.72

45.24

μm

0 5 10 15

CMPS number

0

0.05

0.1

0.15

0.2

Frequency

Original (56)

Re-construction (56)

0 2 4 6 8 10 12 14 16 18

CMPS number

0

0.05

0.1

0.15

0.2

Frequency

Original (56)

Re-construction (56)
39

The re-construction of bag 4 bullet 8 land 1

5 little changed LEA results

The re-construction of bag 6 bullet 6 land 2

0

200

400

-11.972

-6.131

-4

0

4

6.227

12.407

μm

0 200 400 600 800 1000 1200

Pixel

0

200

400

Pixel

-11.972

-4.948

-2.5

0

2.5

4.987

12.691

μm

0

100

200

300

400

-21.12

-12.28

-7.5

0

7.5

12.75

27.62

μm

0 200 400 600 800 1000 1200

Pixel

0

100

200

300

400

Pixel

-21.01

-12.67

-7.5

0

7.5

13.25

30.57

μm

0 5 10 15

CMPS number

0

0.05

0.1

0.15

0.2

0.25

0.3

Frequency

Original (56)

Re-construction (56)

0 5 10 15 20

CMPS number

0

0.05

0.1

0.15

0.2

Frequency

Original (56)

Re-construction (56)
40

The re-construction of bag 7 bullet 7 land 6

5 little changed LEA results

0

200

400

-14.969

-7.707

-4

0

4

7.731

15.692

μm

0 200 400 600 800 1000 1200

Pixel

0

200

400

Pixel

-11.777

-7.131

-4

0

4

7.23

15.977

μm

0 5 10 15 20 25

CMPS number

0

0.05

0.1

0.15

0.2

0.25

Frequency

Original (56)

Re-construction (56)