Guidelines for Trigger Pull Analysis Page 1 of 3 Adopted 11/04/2006

GUIDELINES FOR TRIGGER PULL ANALYSIS

1.0 Objective/Introduction

The objective of the following guidelines is to identify the essential elements

suggested for use in the measurements of firearm trigger pulls and review the

established trigger pull protocols (methodology and instrumentation).

2.0 Definitions/Terminology

Standard terminology and methodologies from sources such as the National Rifle

Association (NRA), Association of Firearm and Tool Mark Examiners (AFTE)

Procedures Manual, the AFTE Glossary, firearm manufacturer manuals, and

equipment manuals should be used in the measurement of trigger pulls.

3.0 Equipment/Supplies

Proper equipment will be used and checked for acceptable accuracy when

appropriate.

3.1 Equipment and supplies may include:

3.1.1 Arsenal weights or dead weights

3.1.2 Spring Gauge

3.1.3 Automated trigger pull device, e.g. TriggerScanTM

3.1.4 Force Gauge

3.2 Equipment utilized for trigger pull measuring should be initially calibrated,

followed by periodic calibration, as defined by individual laboratory protocols

and/or manufacturers documentation.

4.0 Concepts

4.1 Trigger pull examination is a tool in the assessment of a firearm’s safety

system, condition, and factory specifications.

4.2 Consistency in methodology is crucial in the evaluation of data.

4.3 Conducting the trigger pull test in accordance with written protocol is essential

to accurate, reproducible results.
Guidelines for Trigger Pull Analysis Page 2 of 3 Adopted 11/04/2006

5.0 Safety Considerations

General laboratory safe firearm handling protocols should be followed.

6.0 Testing of Objective 1.0

Arsenal weights, spring and digital gauges of various designs and TriggerScanTM

were tested employing various firearm types.

7.0 Testing Results of Objective 1.0

No significant variation between the various trigger pull measuring devices was

observed.

8.0 Conclusions

8.1 Procedures to conduct trigger pull examinations should include, but are not

limited to: manufacturer operating manuals, AFTE Procedures Manual, NRA

guidelines, and laboratory protocols, etc.

8.2 Laboratory protocols should address:

8.2.1 calibration of instruments

8.2.2 methods – slow, consistent application of pressure

8.2.3 orientation of equipment – proper alignment of measuring device to

firearm

9.0 References:

1. Cunningham, Jordan., "Accuracy Testing on Dvorak Instruments’ Trigger-ScanTM

System," AFTE Journal, Volume 32, Number 4, Fall 2000, pp. 364-366.

2. Association of Firearms and Toolmark Examiners Procedures Manual, Trigger Pull

Examination – Standard Trigger Weights (FA-I-4), Version July 9, 2001

3. Association of Firearms and Toolmark Examiners Procedures Manual, Trigger Pull

Examination – Spring Gauge (FA-I-5), Version July 9, 2001

4. Association of Firearms and Toolmark Examiners Procedures Manual, Trigger Pull

Examination – Automated Systems (FA-I-6), Version July 9, 2001

5. AFTE Glossary, Fourth Edition (Trigger Pull Reference)

6. Dillon, John H., “The Trigger ScanTM System – Microprocessor Technology Applied to

Precision Trigger Pull Analysis” AFTE Journal, Volume 31, Number 2, Spring 1999, pp.

123-130.

7. Koffman, Avi, Silverwater, Howard, Argaman, Uri, Hocherman, Gil, and Shoshani,

Ezra, “TriggerScanTM Computerized Trigger Pull System,” AFTE Journal, Volume 29,

Number 4, Fall 1999, pp. 449 – 456.

8. Lomoro, Vincent, “A Statistical Analysis of Trigger Pulls” AFTE Journal, Volume 18,

Number 1, Winter 1986, pp.
Guidelines for Trigger Pull Analysis Page 3 of 3 Adopted 11/04/2006

9. Rios, Ferdinand and Thorton, John, “Static vs. Dynamic Determination of Trigger Pull”,

AFTE Journal, Volume 16, Number 3, July 1984, pp. 84-86.

10. Thompson, Evan., “Preloaded vs. Normal Trigger Pull Weights” AFTE Journal, Volume

27, Number 1, Spring 1995, pp. 62 – 64.

11. Gamboe, Tom, “MAFS Firearms Workshop: Trigger Pull Methods” AFTE Journal,

Volume 18, Number 3, July 1986, pp. 77 – 79.

12. Templin, Reginald, and Nielson, John., “Evaluation of the Effects of Cyanoacrylate

Processing on Pistol and Revolver Trigger Pull” AFTE Journal, Volume 20, Number 4,

Spring 1988, pp. 443 – 445.

13. Unpublished Empirical Trigger Pull Data conducted by the SWGGUN Trigger Pull sub

committee in September 21 – 23, 2004 at the Federal Bureau of Investigation,

Firearms and Toolmark Laboratory, Quantico, Virginia

14. Unpublished Empirical Trigger Pull Data conducted by the SWGGUN Trigger Pull sub

committee in March 29 – 31, 2005 at the Federal Bureau of Investigation, Firearms

and Toolmark Laboratory, Quantico, Virginia

15. Unpublished Empirical Trigger Pull Data conducted by the SWGGUN Trigger Pull sub

committee in June 2005 at the Association of Firearm/Toolmark Examiner 2005

training conference, Indianapolis, Indiana.

Additional Reference Material

1. NRA trigger pull guidelines

2. AFTE Glossary

3. Imada Manual

4. TriggerScanTM Manual

5. Chatillion Manual

6. Static Weights (Brownells)