Standard Test Method for the Examination and 

Comparison of Toolmarks for Source Attribution 

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3 OSAC 2024-S-0002 

4 Standard Test Method for the 

5 Examination and Comparison of 

6 Toolmarks for Source Attribution

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8 Firearms & Toolmarks Subcommittee 

9 Physics/Pattern Interpretation Scientific Area Committee 

10 Organization of Scientific Area Committees (OSAC) for Forensic Science 

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Standard Test Method for the Examination and 

Comparison of Toolmarks for Source Attribution 

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26 

27 Draft OSAC Proposed Standard 

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29 DRAFT OSAC 2024-S-0002 

30 Standard Test Method for the 

31 Examination and Comparison of 

32 Toolmarks for Source Attribution 

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34 Prepared by 

35 Firearms & Toolmarks Subcommittee 

36 Version: 1.0 

37 November2023 

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40 Disclaimer: 

41 This OSAC Proposed Standard was written by the Organization of Scientific Area Committees 

42 (OSAC) for Forensic Science following a process that includes an open comment period. This 

43 Proposed Standard will be submitted to a standards developing organization and is subject to 

44 change. 

45 There may be references in an OSAC Proposed Standard to other publications under development 

46 by OSAC. The information in the Proposed Standard, and underlying concepts and methodologies, 

47 may be used by the forensic-science community before the completion of such companion 

48 publications. 

49 Any identification of commercial equipment, instruments, or materials in the Proposed Standard 

50 is not a recommendation or endorsement by the U.S. Government and does not imply that the 

51 equipment, instruments, or materials are necessarily the best available for the purpose. 

52 To be placed on the OSAC Registry, certain types of standards first must be reviewed by a 

53 Scientific and Technical Review (STR). The STR process is vital to OSAC’s mission of generating 

54 and recognizing scientifically sound standards for producing and interpreting forensic science 

55 results. The STR shall provide critical and knowledgeable reviews of draft standards or of 

56 proposed revisions of standards previously published by standards developing organizations 

57 (SDOs) to ensure that the published methods that practitioners employ are scientifically valid, and 

58 the resulting claims are trustworthy. 
Standard Test Method for the Examination and 

Comparison of Toolmarks for Source Attribution 

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59 The STR will consist of an independent and diverse panel, including subject matter experts, human 

60 factors scientists, quality assurance personnel, and legal experts, which will be tasked with 

61 evaluating the proposed standard based on a comprehensive list of science-based criteria. 

62 For more information about this important process, please visit our website 

63 at: https://www.nist.gov/topics/organization-scientific-area-committees-forensic64 science/scientific-technical-review-panels. 

65 
Standard Test Method for the Examination and 

Comparison of Toolmarks for Source Attribution 

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66 Foreword 

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68 This document is intended to provide standardized minimum requirements for the microscopic 

69 evaluation, classification, and comparison of toolmarks for source attribution and defines the 

70 minimum requirements for supporting documentation. 

71 Additional documents which contain information related to this standards document include: 

72 ● Standard Scale of Source Conclusions and Criteria for Toolmark Examinations 

73 ● Standard for Verification of Source Conclusions in Toolmark Examinations 

74 ● OSAC Firearms Process Map 

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76 This document was developed to provide standardized minimum requirements for the microscopic 

77 comparison of toolmarks by forensic firearm and/or toolmark examiners for the purpose of source 

78 attribution. 

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102 Keywords: Firearms, toolmarks, comparison, documentation, notes, photography 

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Standard Test Method for the Examination and 

Comparison of Toolmarks for Source Attribution 

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104 Table of Contents 

105 1 Scope ....................................................................................................................................... 6

106 2 Normative References ............................................................................................................. 6

107 3 Terms and Definitions ............................................................................................................. 6

108 4 Requirements ........................................................................................................................... 8

109 Appendix A ................................................................................................................................... 16

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Standard Test Method for the Examination and 

Comparison of Toolmarks for Source Attribution 

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112 1 Scope 

113 This standard provides procedures for the microscopic evaluation, classification, and comparison 

114 of toolmarks for source attribution and defines the minimum requirements for supporting 

115 documentation. Throughout this document, the term “toolmark” is used to refer to both firearm116 produced and non-firearm-produced toolmarks. 

117 2 Normative References 

118 ASB 100-Standard Scale of Source Conclusions Criteria for Toolmark Examinations 

119 3 Terms and Definitions 

120 For the purposes of this document, the following definitions and abbreviations apply: 

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122 3.1

123 class characteristics 

124 Observable features of a specimen which indicate a restricted group source. They result from 

125 design and manufacturing decisions that are within acceptable tolerances and are, therefore, 

126 determined prior to manufacture. 

127 3.2 

128 classification 

129 The determination of a specimen’s discernible class characteristics, thereby defining the class to 

130 which it belongs (e.g., a .45 caliber bullet bearing five groove impressions and right twist). 

131 3.3 

132 comparison 

133 The side-by-side examination of two toolmarks. This comparison may be performed 

134 microscopically or macroscopically, as needed. 

135 3.4 

136 conclusion (i.e., source conclusion) 

137 The interpretation resulting from the comparison of two toolmarks. 

138 3.5 

139 consulting examiner / consultation 

140 An examiner who, at the request of the primary examiner, provides guidance/opinion/advice to the 

141 primary examiner in regard to an examination. When the consultation is in regard to a source 

142 conclusion, it occurs prior to that conclusion being reached by the primary examiner. 

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Standard Test Method for the Examination and 

Comparison of Toolmarks for Source Attribution 

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144 3.6 

145 E3CV 

146 Acronym for Evaluation, Classification, Comparison, Conclusion, Verification. A manner of 

147 describing the methodology employed by a Firearm and Toolmark Examiner when conducting a 

148 toolmark comparison for source attribution. 

149 3.7 

150 evaluation 

151 The assessment of a specimen for features to determine its suitability for further classification 

152 and/or comparison. 

153 3.8 

154 examiner 

155 The qualified firearm and toolmark examiner responsible for conducting a toolmark examination, 

156 reaching source conclusions, and authoring a report. This person may also be referred to as the 

157 “primary examiner” with regards to verifications. 

158 3.9 

159 exemplar 

160 A toolmark produced by a known tool. Exemplars may also include a cast of a tool working 

161 surface. Exemplars are commonly referred to as “test marks” or, in the case of firearms, “test 

162 fires”. 

163 3.10 

164 individual characteristics 

165 Marks produced by the random imperfections or irregularities of tool surfaces. These random 

166 imperfections or irregularities are produced incidental to manufacture and/or caused by use, 

167 corrosion, or damage. 

168 3.11 

169 light comparison microscopy (LCM) 

170 The use of connected optical microscopes to evaluate/compare microscopic features on two 

171 different specimens. 

172 3.12 

173 questioned toolmark 

174 A toolmark produced by an unknown tool. Also sometimes referred to as an “unknown”. 

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Standard Test Method for the Examination and 

Comparison of Toolmarks for Source Attribution 

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177 3.13 

178 subclass characteristics 

179 Toolmarks produced by a single tool that repeat with little, if any, change on a limited series of 

180 sequentially manufactured items. These types of characteristics are not determined prior to 

181 manufacture, and are more restrictive than class characteristics (i.e., a subset of the class).

182 3.14 

183 tool 

184 The harder of two objects which, when brought into contact with each other, result in the softer 

185 object being marked by the harder object. 

186 3.15 

187 toolmark 

188 A mark caused when a tool makes contact with an object. 

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190 3.16 

191 verification 

192 Performing subsequent testing to ascertain if the results are concordant. 

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194 3.17 

195 verifier 

196 The qualified firearm and toolmark examiner tasked with performing the verification as described 

197 in 3.16. 

198 3.18 

199 virtual comparison microscopy (VCM) 

200 A method of toolmark analysis involving the use of hardware and software to allow side-by-side 

201 comparison of 3D topography data. 

202 4 Requirements 

203 4.1 Background 

204 A laboratory shall have procedures in place prior to beginning evaluations or comparisons of 

205 toolmarks. Comparisons may be performed between two or more questioned toolmarks or between 

206 exemplars and questioned toolmarks. Most toolmark comparison casework follows a general 

207 methodology of Evaluation, Classification, Comparison, Conclusion and Verification (E3CV). 

208 4.2 Evaluation and Classification of Toolmarks or Known Tools 

209 4.2.1 Evaluation 
Standard Test Method for the Examination and 

Comparison of Toolmarks for Source Attribution 

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210 The tool and/or toolmark shall be evaluated for the presence of discernable class characteristics, 

211 subclass characteristics, and individual characteristics that may assist in source conclusions. The 

212 physical specimen should be marked with a unique identifier. 

213 4.2.1.1 If no class, no subclass, and no individual characteristics are discernable, the specimen has 

214 no value for classification or comparison. The specimen may be suitable for other analyses not 

215 addressed in this document.

216 4.2.1.2 If class, subclass, and/or individual characteristics are discernable, then the specimen may 

217 be suitable for further classification and/or comparison. 

218 4.2.2 Classification

219 Document the relevant class characteristics of the tool or toolmark. 

220 Class characteristics may include, but are not limited to: 

221 4.2.2.1 Non-Firearm Tool/Toolmark Class Assessment 

222  Type of tool 

223  Design characteristics of the tool (features determined prior to manufacture) 

224  Tool action type 

225  Manufacturing process of the tool working surface 

226  Dimensions of tool working surfaces 

227  Dimensions of the toolmark 

228  Characterization of marks within the toolmark (e.g., impressed, striated, gross vs. fine 

229 markings, parallel vs. arches, etc.) 

230 4.2.2.2 Firearm Class Assessment 

231  Caliber 

232  Characterization of the toolmarks on the firearm (e.g., parallel breechface marks, 

233 concentric circles on firing pin, etc.) 

234  Manufacturing processes employed (e.g., broach, mill, bead blasting, cast) 

235  Firing pin shape 

236  Firing pin aperture shape 

237  Location and shape of extractor and ejector 

238  Rifling characteristics ((e.g., number of lands and grooves, dimensions of lands and 

239 grooves) 

240  Characterization of toolmarks within a barrel (e.g., longitudinal or circumferential 

241 toolmarks on lands and/or grooves, etc.) 

242 4.2.2.3 Fired/Cycled Ammunition Component Class Assessment 

243 4.2.2.3.1 Bullets 

244  Diameter/caliber 

245  Weight 

246  Design 
Standard Test Method for the Examination and 

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247  Composition 

248  Number of land and groove impressions 

249  Direction of twist 

250  Land impression width 

251  Groove impression width 

252  Rifling profile (conventional or polygonal) 

253 4.2.2.3.2 Cartridge Cases and Fired Shotshells 

254  Caliber/gauge 

255  Breech face marks (e.g., parallel, arced, granular, circular, cross-hatched)

256  Location and shape of extractor and ejector marks

257  Firing pin impression shape

258  Firing pin aperture shape

259  Headstamp

260  Design (e.g., type and size of shot, case material, primer material)

261  Feed/cycling marks

262 In some instances, it may not be possible to determine class characteristics due to the condition of 

263 the specimen under examination. 

264 4.2.2.4 Comparison of Class Characteristics 

265 If discernible class characteristics are in agreement, continue with further examination and 

266 comparison. If discernible class characteristics are in disagreement, a conclusion of exclusion 

267 shall be reached. 

268 4.2.3 Subclass Characteristic Assessment 

269 Examine and evaluate the tool working surface(s) or the toolmark for subclass characteristic 

270 potential. 

271 4.2.3.1 Evaluation of Tool 

272 All surfaces used as a basis for a source conclusion other than a class exclusion shall be evaluated 

273 for the potential presence of subclass characteristics. The manufacturing method(s) and its 

274 potential for subclass characteristics shall be considered. 

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276 The following attributes may be indicative of the potential for subclass characteristics: 

277  Coarse/gross detail 

278  Mold marks/part lines 

279  Stamping marks 

280  Repeating pattern 

281  Marks that continue from one end of the working surface to the opposite end 

282  Uniform spacing of marks 

283 
Standard Test Method for the Examination and 

Comparison of Toolmarks for Source Attribution 

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284 The following non-exhaustive list of attributes are indicative of a working surface that contains or 

285 produces individual characteristics: 

286  A working surface that is the result of the intersection of two polished or machined surfaces 

287 (e.g., firing pin aperture edge) 

288  A machined working surface bearing a linear pattern that includes discontinuous and/or 

289 non-parallel features. 

290  A machined working surface bearing isolated features that are the result of random chip 

291 separation, chatter, etc. 

292  A working surface bearing features that are the result of hand filing, grinding, media 

293 blasting, tumbling, or other abrasive or burnishing finishing processes. 

294  A working surface bearing post-manufacturing defects from damage, use, corrosion, etc. 

295  A working surface bearing features that are the result of non-axial drilling, reaming, or 

296 honing processes (e.g., drilling/reaming marks on rifling lands, reaming marks in chamber, 

297 reaming marks in forcing cone) 

298  A working surface bearing features that are the result of electrochemical or electrical 

299 discharge machining (i.e., the presence of pitting on the work surface) 

300 4.2.3.2 Evaluation of Toolmark 

301 All surfaces used as a basis for a source conclusion other than a class exclusion shall be evaluated 

302 for the potential presence of subclass characteristics. When possible, assess the manufacturing 

303 method(s) and its potential for subclass characteristics. 

304 The following attributes may be indicative of the potential for subclass characteristics: 

305  Coarse/gross detail 

306  Mold marks/part lines 

307  Repeating pattern 

308  Marks that continue from one end of the working surface to the opposite end. 

309  Uniform spacing of marks 

310 The following non-exhaustive list of attributes are indicative of individual characteristics: 

311  A toolmark that is the result of the intersection of two polished or machined surfaces (e.g., 

312 firing pin aperture shear) 

313  A toolmark bearing linear features that are discontinuous and/or non-parallel. 

314  A toolmark bearing isolated marks such as random chip separation, chatter, etc. 

315  Toolmarks that resulted from hand filing, grinding, media blasting, tumbling, or other 

316 abrasive or burnishing processes. 

317  Toolmarks bearing characteristics that are indicative of post-manufacturing defects such as 

318 damage, use, corrosion, etc. 

319 4.2.3.3 To the extent possible, evaluate the impact of the subclass characteristics on the ability to 

320 reach source conclusions. An opinion of the same source shall not be based solely on agreement 

321 of potential subclass characteristics. Subclass characteristics indicate a restrictive group only. 
Standard Test Method for the Examination and 

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322 4.3 Preparation of Exemplar (Test Marks) 

323 Exemplars are produced from tools for comparison purposes. Exemplars may include toolmarks 

324 produced by a tool and/or casts of a tool working surface. 

325 4.3.1 Preparation of Exemplars from Non-Firearm Tools 

326  Determine which working surface(s) or area(s) of the working surface of the tool may have 

327 been used. Consider physical constraints and the presence of trace materials that may 

328 indicate the area of the surface used. 

329  Select the appropriate test material, considering the relative hardness of the tool working 

330 surface and the test material so as to minimize damage to the tool working surface and 

331 successfully reproduce toolmarks for comparison. Typically, a softer material is initially 

332 selected; however, it may be necessary to select a harder material (e.g., progressing from 

333 lead to copper to steel) to obtain suitable exemplars for comparison. 

334  Attempt to determine and replicate the tool-substrate interaction that occurred when the 

335 questioned toolmark was created (e.g., angle, pressure, direction). 

336  Label exemplars in accordance with laboratory policy. If possible, the physical specimens 

337 should be directly marked with a unique identifier. 

338  As an alternative, or in addition, to producing toolmark exemplars, it may be desirable to 

339 produce casts of the tool working surface. 

340  In situations when the tool will be directly compared to the toolmark, the preparation of 

341 exemplars may not be necessary. 

342  Exemplars shall be preserved, whether retained in the laboratory, returned to the submitting 

343 agency, or some other mechanism. 

344 4.3.2 Preparation of Exemplars from Firearms 

345  Select appropriate ammunition for test firing. In order to minimize variables, the 

346 ammunition selected should be the same caliber, design, and composition as the specimens 

347 to be compared. 

348  Select an appropriate recovery medium that will minimize damage to any test-fired bullets. 

349  Conduct test firing. 

350  Label exemplars in accordance with laboratory policy. If possible, the physical specimens 

351 should be directly marked with a unique identifier. 

352  As an alternative, or addition to, producing test-fired exemplars, it may be desirable to 

353 produce casts of the firearm working surface(s). 

354  If the firearm is nonfunctional, exemplars of specific working surfaces may need to be 

355 created using a suitable medium (e.g., lead, silicone cast, etc.). 

356  In situations when the working surface will be directly compared to the toolmark, the 

357 preparation of exemplars may not be necessary. 

358  Exemplars shall be preserved, whether retained in the laboratory, returned to the submitting 

359 agency, or some other mechanism. 

360 4.4 Comparison of Microscopic Toolmarks 

361 4.4.1 Microscopic Comparison 

362  Select the type of microscopic evaluation/comparison to be performed (e.g., Light 
Standard Test Method for the Examination and 

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363 Comparison Microscopy and/or Virtual Comparison Microscopy) in accordance with 

364 laboratory policy. 

365  Orient specimens for comparison. 

366  Use a systematic process to ensure the identity of the specimens being examined. The 

367 process shall include the confirmation of the unique identifiers of the specimens. 

368  Optimize magnification. A variety of magnification levels should be used when comparing 

369 toolmarks. Typically, lower magnification is used first and magnification may be increased 

370 as needed to observe relevant detail. The magnification should be the same for both 

specimens.1 371 

372  Optimize lighting. Oblique lighting is usually preferred. Lighting may be varied during 

373 the course of the examination. 

374 4.4.2 Exemplar Comparisons 

375 Exemplars produced by the suspected tool should be microscopically intercompared to determine 

376 which markings reliably reproduce with sufficient detail for comparison to questioned toolmarks. 

377 Exemplars in varying substrates may be evaluated to determine the effects of the substrate on the 

378 toolmark. 

379 If subclass marks are observed on the tool/firearm, then subclass influence shall be considered 

380 when comparing exemplars. Subclass on the tool/firearm does not necessarily preclude the use of 

381 that area for source conclusion. The interaction between the working surface and the item being 

382 marked influences whether subclass marks on the tool/firearm are directly transferred or if the 

383 resulting toolmark has no subclass influence. Comparing the toolmarks on the tool/firearm to the 

384 resulting toolmark(s) on the exemplar can assist with this assessment. Toolmarks that are believed 

385 to be subclass characteristics shall not be used for identification conclusions. 

386 4.4.3 Questioned Toolmark Comparisons 

387 Comparison may be performed between two or more questioned toolmarks (for common source), 

388 or between exemplars and questioned toolmarks (for specific source). 

389 Compare areas of interest and document the specific areas (e.g., breech face, firing pin) and any 

390 significant agreement and/or disagreement observed. 

391 The entirety of the toolmark or combination of toolmarks shall be considered. Examiners shall 

392 consider all similarities and differences observed prior to reaching a conclusion. 

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 In situations of a distorted specimen compared to an undamaged one, minor adjustments to the magnification may be 

appropriate to account for distortion. If done, this shall be recorded in the case record. 
Standard Test Method for the Examination and 

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393 During the comparison process the following factors may also be considered: 

394  Adjustments to angle and/or type of lighting 

395  Need for additional exemplars 

396  Enhancement techniques (e.g., magnesium fuming, cast of deep firing pin impression) 

397  Consultation with another examiner(s) 

398 

399 4.5 Conclusion 

400 SEE CONCLUSIONS DOCUMENT 

401 4.6 Verification 

402 SEE VERIFICATION DOCUMENT 

403 4.7 Documentation 

404 The evaluation, classification, subclass characteristic assessment, and comparison shall be 

405 documented. Documentation must include depictions or descriptions of the observations to the 

406 extent that another examiner, without the benefit of the specimens themselves, can review the case 

407 record and understand what analysis was conducted, and the basis for any conclusions. All 

408 documentation shall be retained per laboratory policy. 

409 4.7.1 Documentation of Evaluations that result in a determination of no value for comparison 

410 shall include the basis for that determination (e.g., no class or individual characteristics present). 

411  Written notes are sufficient and may be supplemented with photographs. 

412  Determinations of value are implied if the examiner moves on to further 

413 classification/comparison, and thus do not need to be explicitly stated/documented. 

414  If it is determined an item is of value for further comparison but is not further classified 

415 and/or compared (i.e., no other samples for comparison), the “of value” determination and 

416 the reason for no further analysis shall be documented. 

417 4.7.2 Documentation of Classification examinations shall include: 

418  The relevant class characteristics of each item. 

419  If certain class characteristics cannot be determined (e.g., a bullet fragment, partial 

420 toolmark), the documentation shall include the reason(s). 

421 o If a range of classes can be determined, the documentation shall include reasons for 

422 the determination. 

423  Written notes are sufficient and may be supplemented with photographs. 

424 4.7.3 Documentation of Subclass characteristic assessment shall include: 

425  The surfaces that were assessed for subclass and the observations that support the 

426 conclusions drawn from that assessment. 

427  The method of assessment, such as the microscopic assessment of the tool, use of casts, 

428 borescope, etc. 

429  Written notes are sufficient and may be supplemented with photographs. 

430 
Standard Test Method for the Examination and 

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431 4.7.4 Documentation of Comparison examination shall include: 

432  Exemplars: areas of the specimens compared and observations. 

433  Questioned toolmarks: areas of the specimens compared, observations, and conclusion(s) 

434 reached. 

435 ○ Same-source conclusions: photographs and/or VCM screenshots with 

436 supplemental descriptions of the agreement of individual and/or class 

437 characteristics. 

438 ○ Inconclusive conclusions: descriptions of agreement/disagreement or absence of 

439 individual and/or class characteristics. These descriptions may be supplemented 

440 with photographs and/or VCM screenshots. 

441 ○ Different-source conclusions: Descriptions of the disagreement of individual 

442 and/or class characteristics. These descriptions may be supplemented with 

443 photographs and/or VCM screenshots. 

444 4.7.4.1 It shall be clear from the documentation which pair-wise comparisons were performed, as 

445 well as any additional measures taken (e.g., enhancement techniques, need for additional 

446 exemplars), so that another examiner can perform the same pair-wise comparisons under similar 

447 conditions. The documentation shall include which specific exemplar(s) was used, when 

448 applicable. 

449 4.7.4.2 A statement of conclusion alone, without supporting documentation, is insufficient. 

450 4.7.5 While it is recognized that photographic documentation (e.g. photographs, VCM 

451 screenshot) cannot be held in equal standing with live comparison observations, photographs shall, 

452 to the extent possible, document the observations that formed the basis for the reported 

453 conclusions. 

454 4.7.5.1 Conclusions of identification shall be documented with photographs which demonstrate 

455 the toolmark agreement observed in all areas of the specimens used for reaching the conclusion. 

456 4.7.5.2 A photograph of one comparison may be used as documentation for multiple comparisons 

457 as long as what is depicted in the image is representative of the toolmark(s) and level of agreement 

458 observed in all comparisons. 
Standard Test Method for the Examination and 

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459 Appendix A 

460 (informative) 

461 Bibliography 

462 

463 1) ANSI/ASB Best Practice Recommendation 068, Safe Handling of Firearms and 

464 Ammunition. 2020. 1st. Ed. 

465 2) ANSI/ASB Standard 093, Standard Test Method for the Forensic Examination and Testing of 

466 Firearms. 2020. 1st. Ed. 

467 3) Nichols R., “Subclass Characteristics: From Origin to Evaluation” AFTE Journal. Spring, 

468 2018. 50(2) pages 68-88.