NIST Bullet SRM 2460 Replication and Validation 

Using an Improved Vacuum Casting Method and 

Potential Evidentiary Use

T. Brian Renegar, Alan Zheng, Robert M. Thompson, John Song, 

James Yen, Dr. Theodore Vorburger

Semiconductor & Dimensional Metrology Division

Law Enforcement Standards Office

November 28, 2012
Outline

SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 2

• Introduction

• Motivation

• Casting procedure overview

• Validation of process - correlation analysis

• Decay factor study

• Possible evidentiary uses 

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Introduction

•Casting of impressions, toolmarks, and 

firearm surfaces are employed as a 

means to transport evidence and 

preserve surface features.

•Casts are routinely used as primary 

evidence for analysis and comparison 

where direct examination would be 

impractical or impossible.

SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 3

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Introduction

• The NIST SRM 2460 Standard Bullet is 

successfully being used as a quality control 

standard in forensic laboratories

• The bullet surfaces are well characterized &

validated using surface profile analysis.

SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 4

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Motivation

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• A total of 40 NIST SRM2460 Standard 

Bullets were produced. 

• Due to the complex manufacturing 

process, they are expensive ($2120 ea.) 

and time consuming to manufacture. 

• Almost sold out. 

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Motivation

• Need an inexpensive and less time consuming method to 

replenish the Standard Bullet. 

• Requirements: 

 Needs to retain the same surface topography 

quality as the original standard bullets 

 Color/translucency properties must be compatible 

with microscope imaging

 Durable

Polymer replication using vacuum casting technique could 

potentially be used to restock the Standard Bullets

SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 6

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European Research

“Vorrichtung zum Abformen von Hülsen und 

Geschossen unterschiedlicher Kaliber”

Alfons Koch, 2010

(Patent application DPMA DE 10 2005 039 

823.5-15)

BKA/NIST signed MOU in 2011

SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 7

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Vacuum Casting Technique

- Replication container

A replication container was fabricated to house the master 

bullets during the silicone molding phase. 

SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 8

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Mixing silicone Vacuum-degassing in desiccator

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Vacuum Casting Technique

- Step 1: Silicone Mold 

Pouring silicone into replication rig 2nd vacuum-degas
Vacuum Casting Technique

- Removing the silicone mold from the replication rig

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SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 
Vacuum Casting Technique

- Step 2: Polyurethane Replica

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Mixing polyurethane with dye, and vacuum-degas

Use a dropper to fill mold with urethane. Vacuum-degas and let cure
Vacuum Casting Technique

- Removing the cured polyurethane replica bullets from 

the silicone mold

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Carefully separate the silicone from the urethane replicas and then 

remove the replicas with needle nose pliers. The bullet standoff in 

the replication rig will avoid contact with the striated regions of the 

bullets, avoiding any damage. 

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SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 
First Replication (before vacuum degassing)

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Silicone Mold

Urethane Replica

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SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 
First Replication (before vacuum degassing)

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SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 

(5X Optical Image)

Quality control of micro-bubbles needs to be addressed
Improvements to process

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• Vacuum / degassing 

using a belt driven 

“roughing” pump during

mixing process

5 x 10-2 Torr

(6.5 x 10-5 atmosphere)

• Changes to silicone & polyurethane materials

 Reduced viscosity

 Longer working time

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SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 
Improved Procedure

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(5X Optical comparison)

Is it Real? Or is it Memorex?

 Replica from Mold 13a Original SRM 2460-038

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SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 
Improved Procedure

Even stylus traces from original SRM 2460-038 are 

visible in the replication. These features are submicrometer in scale.

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SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 
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Close-up images 

of Standard 

Bullet replicas

SRM 2460-038
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Stylus Measurement of the Replica Bullets

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Example of CCF Correlation Program

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VERY High CCF value of 99.37% means that the Replica is 

virtually identical to the Master Bullet

SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 

Stylus profile comparison of virtual signature to Replica
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Decay Factor: Time 

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Measurement Date CCFmax % Lateral Scaling

5/29/2012 99.37 1.0055

5/30/2012 99.41 1.0060

5/31/2012 99.47 1.0050

6/1/2012 99.50 1.0055

6/4/2012 99.39 1.0055

6/5/2012 99.41 1.0050

6/6/2012 99.45 1.0050

6/7/2012 99.46 1.0055

6/11/2012 99.48 1.0055

6/12/2012 99.51 1.0055

6/13/2012 99.49 1.0055

6/14/2012 99.45 1.0055

6/18/2012 99.47 1.0050

6/19/2012 99.46 1.0050

6/20/2012 99.49 1.0050

6/21/2012 99.49 1.0050

6/22/2012 99.47 1.0050

11/26/2012 99.41 1.0050

High CCF

6 months 

later

Mold 10, Bullet # 15

Virtual Standard vs Each Consecutive Date
Decay Factor: Sibling Replications 

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SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 

Multiple replicas made from

a single mold.
Decay Factor: Sibling Replications - CCF Results

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Sibling Replication # CCFmax % Lateral Scaling

1 99.30 1.0045

2 99.32 1.005

3 99.41 1.005

4 99.16 1.005

5 99.20 1.0045

6 99.25 1.003

7 98.72 1.004

8 98.22 1.004

9 98.38 1.0045

10 97.98 1.0045

11 97.45 1.005

12 97.39 1.005

13 97.17 1.0045

14 97.09 1.0045

15 93.42 1.0035

Replicas from Mold # 9, Bullet 038, Land 1
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2460-038

Master

Mold #9

Replica 1

Mold #9

Replica 3

Mold #9

Replica 6

Mold #9

Replica 9

Mold #9

Replica 12

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SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 

Sibling Replications – Optical Comparisons
Decay Factor: Generation Test

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SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 

Each replica is used to create a new mold

Master Bullet #’s 17, 32, & 38 used to create first mold (13a)
Decay Factor: Generation Test

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SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 

Close-up of Generation Replicas

From Master Bullet # 038

Mold 13a Mold 13b Mold 13c Mold 13d

Note: Standoff in replication rig reproduces itself during each casting cycle
Decay Factor: Generation Test – CCF Results

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Generation # CCFmax % Lateral Scaling

1 (Mold 13a) 99.59 1.004

2 (Mold 13b) 99.41 1.0095

3 (Mold 13c) 99.45 1.014

4 (Mold 13d) 99.43 1.019

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SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 

Note: Each urethane replica shrinks by 0.4 - 0.5%.

This is a compounding effect from generation to generation.

Replicas from Molds 13_, Bullet 038, Land 1
Generation Test – Optical Comparisons

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2460-038

Master

Mold #13a

(1st Generation)

Mold #13b

(2nd Generation)

Mold #13c

(3rd Generation)

Mold #13d

(4th Generation)

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SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 
Possible Evidentiary Uses

• Inter-laboratory transfer of bullet (and 

cartridge case) evidence replicas for 

comparisons.

Logistics and chain of custody issues with 

transferring actual evidence are alleviated

• International evidence transfer.

• Large proficiency test production

• Eliminates sample variation in production runs. 

• Pre-evaluated samples representative of 

casework difficulty can be produced.

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SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 
Future Work

• Improve Bullet Replicas

 Testing of release agents, hydrophobic 

coatings, etc. to reduce mold tearing from 

successive replications.

 Utilize pressurization in conjunction with 

vacuum-degassing during silicone/urethane 

curing.

 Durability testing of polymer replicas 

(resistance to abrasives, dirt, oil, solvents, 

etc.)

• Replication of Cartridge Cases

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SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 
Acknowledgements

The funding for this research was partly 

provided by the U.S. National Institute 

of Justice (NIJ) through the Office of 

Law Enforcement Standards (OLES) at 

NIST.

31
T. Brian Renegar

National Institute of Standards and Technology

100 Bureau Drive, Mail Stop 8212

Gaithersburg, MD 20899-8212

(301) 975-4274

brenegar@nist.gov

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Thank you!

Questions?

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SEMICONDUCTOR & DIMENSIONAL METROLOGY DIVISION | LAW ENFORMCEMENT STANDARDS OFFICE 
Previous Research

• “The Production of Replicas of Bullets and Cartridges”, by Geradts, Kreijzer, & C. Van Brakel, 

Netherlands Forensic Science Laboratory.

• Developed procedures to counter shrinkage effects using modern casting materials.

• Potential transfer of evidence in EU.

Reference: AFTE Vol 28, No1 Jan 1996 

• “Casting of Complex Stereometric Samples for proficiency Tests in Firearm & Toolmark

Examinations” Kock & Katterwe, BKA Germany.

• Technique described in the production of a large inter-laboratory proficiency test for bullet identification.

• Evaluated new materials and adapted procedures.

Reference: AFTE Vol 39 No4 Fall 2007

• “Topography measurements for determining the decay factors in surface replication” Song, 

Rubert, Zheng & Vorburger; NIST.

• Developed procedures to test and measure the decay factor in the replication of surface topography.

Reference: Proceedings of ISMTII 2007 MST11

• “Topography Measurements and Performance Comparisons between NIST SRM 2460 Standard 

Bullet Masters and BKA Bullet Replicas”, Song, J., Vorburger, T.V., Thompson, R., Ballou, S., 

Zheng, A., Renegar, T.B., Silver, R., Ols, M., W. Wenz, A. Koch, M. Braune, A. Lohn, AFTE 

Journal, 44, 3, 2012, pp.201-217.

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