From United States v. Glynn, 2008 U.S. Dist. LEXIS 72505 (S.D.N.Y. Sept. 22, 2008) (Rakoff, J.):

Building on a ruling it had made two weeks earlier in another trial involving ballistics testimony, United States v. Damian Brown et al., 05 Cr. 538, th[is] Court, following a "Daubert" hearing, ruled from the bench that Valenti could not testify that ballistics was a "science," nor could he claim that he reached his conclusions to any degree of "certainty," whether "ballistic certainty" or otherwise, see tr. 6/30/08 at 907. The Court further ruled, however, that Valenti's methodology was sufficiently reliable that he could give an opinion that it was at least "more likely than not" that the bullet and casings came from the guns in question. See id. at 1000. ***

The Supreme Court made clear in Daubert that no purportedly scientific expert testimony could be admitted unless it met certain rigorous requirements. See Daubert , 409 U.S. at 593-94 (directing courts to examine: (1) whether the expert's theory or technique "can be (and has been) tested"; (2) "whether the theory or technique has been subjected to peer review and publication"; (3) "the known or potential rate of error" in the theory's application and "the existence and maintenance of standards controlling the technique's operation"; and (4) the "general acceptance" of the theory or technique in the relevant scientific community). In Kumho Tire, however, the Court also made clear that while the basic requirements of reliability — as they are now articulated in Rule 702 — apply across the board to all expert testimony, the more particular standards for scientific evidence need not be met when the testimony offered does not purport to be "science." See Kumho Tire, 526 U.S. at 151-52. This distinction was well-illustrated in Judge Louis Pollak's well-known decisions regarding fingerprinting evidence, in which he held in an initial opinion that fingerprinting did not rest on sufficiently "scientific" principles to be admitted under Daubert but subsequently held that the technique afforded sufficient practical reliability to be admissible, subject to the court's oversight, as expert testimony. See United States v. Plaza, 179 F. Supp. 2d 492, 516-18 (E.D. Pa. 2002); United States v. Plaza, 188 F. Supp. 2d 549, 576 (E.D. Pa. 2002) (granting motion for reconsideration).***

[B]allistics comparison lacks defining standards to a degree that exceeds most other kinds of forensic expertise. For example, whereas both a ballistics examiner and a fingerprint examiner are ultimately called upon to make a subjective judgment of whether the agreement between two pieces of evidence is "sufficient" to constitute a "match," a fingerprint examiner may not declare a match unless a pre-specified number of "points" of similarity exist between the two samples, see, e.g., United States v. Mitchell, 145 F.3d 572, 575 (3d Cir. 1998); Plaza, 188 F. Supp. 2d at 564. Although attempts been made to introduce similar minimum standards and "protocols" into ballistics analysis, such attempts have not yet met with general acceptance and, in any event, were not applied by the examiners [before this Court]. ***

The Court therefore concluded that to allow Detective Valenti, or any other ballistics examiner, to testify that he had matched a bullet or casing to a particular gun "to a reasonable degree of ballistic certainty" would seriously mislead the jury as to the nature of the expertise involved. ***

The Court therefore determined *** that the ballistics examiners in those cases would be permitted to testify only that a firearms match was "more likely than not," thereby satisfying Rule 401 without overstating the capacity of the methodology to ascertain matches. ***

In Glynn, the Court was also persuaded to permit Valenti to add the qualifier "at least," so that his opinion was that the matches were "at least more likely than not." On further reflection, however, this qualifier serves only to add uncertainty to what is otherwise clear-cut: that the opinion has utilized a methodology that permits him to determine, albeit with some subjectivity, that certain markings more likely than not emanated from the same gun. To add the qualifier "at least" is to inject an element of vagueness into this otherwise straightforward conclusion. Accordingly, the ballistics opinions offered at the Glynn retrial may be stated in terms of "more likely than not," but nothing more.