This case returns to our court pursuant to a remand order from the United States Supreme Court following its decision in Melendez-Diaz v. Massachusetts, 129 S. Ct. 2527 (2009) (Melendez-Diaz). See Morales v. Massachusetts, 129 S. Ct. 2858 (2009). In our previous decision, Commonwealth v. Morales, 71 Mass. App. Ct. 587, 588-589 (2008), we affirmed the defendant’s convictions of possession of a firearm with a defaced serial number, G. L. c. 269, § 11C; unlawful possession of ammunition, G. L. c. 269, § 10(A); unlawful possession of a firearm, G. L. c. 269, § 10(a); and possession of a class A substance (heroin) with intent to distribute, G. L. c. 94C, § 32(a), holding, inter alia, that there was no error in the admission in evidence of a ballistics certificate.
The defendant now argues, in light of the decision in Melendez-Diaz, that the admission of both the ballistics certificate and a drug certificate, without accompanying testimony from the ballistician and lab analyst who produced them, violated his confrontation rights under the Sixth Amendment to the United States Constitution and constituted error that was not harmless beyond a reasonable doubt. We agree in part and reverse three of the defendant’s four convictions.
Facts. Acting on warrants to arrest the defendant and an allegation that the defendant had assaulted his girlfriend, Brock-ton police officers pulled over a vehicle in which the defendant was a passenger. The defendant was removed from the passenger seat, handcuffed, and pat frisked. The police recovered from his person a .40 caliber gun with the serial number scratched off, two magazines containing bullets, a knife, twenty-nine bags of a white powder, a cellular telephone, and $375 in cash. The loaded gun was located at the defendant’s belt line near the small of his back, when seized by the police officer.
The Commonwealth introduced a ballistics certificate at trial, which stated that the gun seized from the defendant was successfully test fired with no malfunction and that the bullets constituted ammunition. The Commonwealth also introduced a certificate of drug analysis, which stated that the twenty-nine bags found on the defendant contained a net weight of 7.83 grams of heroin. At trial, a detective testified that the substance *665seized from the defendant was packaged in a manner consistent with the sale and distribution of heroin.
Discussion. The introduction of the ballistics and drug certificates without accompanying testimony from the ballistician and lab analyst who produced them violated the defendant’s Sixth Amendment right to confront and cross-examine the witnesses against him. See Melendez-Diaz, 129 S. Ct. at 2532. We must now determine whether the erroneous admission of the certificates was harmless beyond a reasonable doubt.1
1. Harmless error standard, a. Federal law. In Chapman v. California, 386 U.S. 18, 21 (1967) (Chapman), the Supreme Court held that Federal law governs whether Federal constitutional errors are harmless. The court ruled that a constitutional error can be harmless if “the beneficiary of a constitutional error . . . prove[s] beyond a reasonable doubt that the error complained of did not contribute to the verdict obtained.” Id. at 24. The court also stated that there was “little, if any, difference” between this standard and the standard articulated in Fahy v. Connecticut, 375 U.S. 85, 86-87 (1963): “The question is whether there is a reasonable possibility that the evidence complained of might have contributed to the conviction.” Ibid.
Two years after Chapman, the Supreme Court decided Harrington v. California, 395 U.S. 250, 254 (1969), and held that “the case against [the defendant] was so overwhelming that we conclude that [the constitutional error] was harmless beyond a reasonable doubt.” While adding the “overwhelming evidence” factor into the harmless error analysis, the court also reaffirmed the test it set out in Chapman. Harrington v. California, 395 U.S. at 254 (“We do not depart from Chapman-, nor do we dilute it by inference. We reaffirm it”).
In Delaware v. Van Arsdall, the Supreme Court confirmed *666that the analysis in Chapman was the standard for determining whether Federal constitutional errors are harmless. 475 U.S. 673, 684 (1986) (“the constitutionally improper denial of a defendant’s opportunity to impeach a witness for bias, like other Confrontation Clause errors, is subject to Chapman harmless-error analysis”). The Van Arsdall Court also set out a list of factors for courts to consider when conducting such a harmless error review, including the over-all strength of the prosecution’s case.2 Ibid.
Chapman remains the touchstone for harmless error analysis. See, e.g., Sullivan v. Louisiana, 508 U.S. 275, 278-279 (1993); United States v. Gonzalez-Lopez, 548 U.S. 140, 157 (2006) (Alito, J., dissenting). Moreover, when conducting a Chapman analysis, the Supreme Court continues to consider whether the admissible evidence in the case is overwhelming. See, e.g., Bundy v. Florida, 479 U.S. 894, 897 (1986) (Marshall, J., dissenting from order denying certiorari); Neder v. United States, 527 U.S. 1, 16-17 (1999).
b. Massachusetts law. The Supreme Judicial Court has stated the harmless beyond a reasonable doubt standard in several ways. See Commonwealth v. Marini, 375 Mass. 510, 520 (1978) (“[I]t would be hard to say that the [error] was without effect on the jury and did not contribute to the verdict”); Commonwealth v. Gilday, 382 Mass. 166, 178 (1980) (“We should set aside the conviction unless we are ‘sure that the error did not influence the jury, or had but very slight effect’ ”), quoting from United States v. Agurs, 427 U.S. 97, 112 (1976); Commonwealth v. Perrot, 407 Mass. 539, 549 (1990) (“The essential question is whether the error had, or might have had, an effect on the jury and whether the error contributed to or might have contributed to the verdicts”); Commonwealth v. Perez, 411 Mass. 249, 260 (1991) (citing two Supreme Court descriptions of the harmless error test, including “whether there is a reasonable possibility that the evidence complained of might have contributed to the *667conviction,” quoting from Chapman, and “whether overwhelming evidence of the defendant’s guilt exists without the erroneously admitted evidence,” citing Milton v. Wainwright, 407 U.S. 371, 372-373 [1972]); Commonwealth v. Depina, 456 Mass. 238, 249 (2010) (“[W]e conclude that the error in this case was harmless beyond a reasonable doubt because the lawfully admitted evidence . . . was so overwhelming as to ‘nullify any effect [the erroneously admitted evidence] might have had on the jury or the verdict’ ”), quoting from Commonwealth v. Tyree, 455 Mass. 676, 704 n.44 (2010).
Despite the varying articulations of the harmless error test set forth in these cases, all cite and rely on the Chapman standard. See Marini, supra at 520; Gilday, supra at 178; Perrot, supra at 548; Perez, supra at 260-261; Depina, supra at 248. Accordingly, in determining whether a constitutional error was harmless, we ask “whether the record establishes ‘beyond a reasonable doubt that the error complained of did not contribute to the verdict obtained.’ ” Commonwealth v. Peixoto, 430 Mass. 654, 660 (2000), quoting from Chapman, supra at 24. See Commonwealth v. Vasquez, 456 Mass. 350, 360-361 (2010).
In answering this question, we consider certain factors discussed by the Supreme Judicial Court in Commonwealth v. Mahdi, 388 Mass. 679, 696-697 (1983), including the weight of evidence of guilt and the frequency of reference to the erroneously admitted evidence. See Peixoto, supra at 660-661. See also Petrillo v. O’Neill, 428 F.3d 41, 45 (1st Cir. 2005), cert. denied sub nom. Petrillo v. Murphy, 547 U.S. 1117 (2006) (“Mahdi expressly incorporates the federal Chapman standard”). The Mahdi factors are neither exclusive nor exhaustive. Mahdi, supra at 697. Commonwealth v. Waite, 422 Mass. 792, 801 n.9 (1996). See Commonwealth v. Vardinski, 438 Mass. 444, 452 (2003) (applying the Van Arsdall factors).
2. Analysis. We turn now to the question whether the Commonwealth has shown beyond a reasonable doubt that the erroneous admission of the certificates here did not contribute to the verdicts. See Commonwealth v. Hollister, 75 Mass. App. Ct. 729, 731 (2009).
a. Drug certificate. “In a case charging a narcotics offense, the Commonwealth must prove beyond a reasonable doubt ‘that *668a substance is a particular drug’ because such proof is an element of the crime charged.” Vasquez, supra at 361, quoting from Commonwealth v. McGilvery, 74 Mass. App. Ct. 508, 511 (2009) . In determining whether the admission of the drug certificate was harmless in that regard, “we ask whether, on the totality of the record before us, weighing the properly admitted and the improperly admitted evidence together, we are satisfied beyond a reasonable doubt that the tainted evidence did not have an effect on the jury and did not contribute to the jury’s verdicts.” Commonwealth v. Tyree, 455 Mass. 676, 701 (2010). See Commonwealth v. Fluellen, 456 Mass. 517, 526-527 (2010).
Therefore, we consider the Commonwealth’s evidence as to the identity of the white powder recovered from the defendant absent the certificate. Not only is the evidence before us not overwhelming, but the record discloses a dearth of independent evidence as to the nature of the substance. Consequently, we cannot conclude beyond a reasonable doubt that the introduction of the drug certificate did not contribute to the defendant’s conviction of possession of a controlled substance with intent to distribute.
The circumstantial evidence that the white powder was packaged in a manner consistent with the sale and distribution of heroin did not render the admission of the drug certificate harmless. Evidence of packaging in a particular manner can be probative of the crime of possession of a controlled substance with intent to distribute, but it can also be probative of the crime of possessing a counterfeit substance with the same intent to distribute. Commonwealth v. Pimentel, ante 236, 239 n.3 (2010) . See G. L. c. 94C, § 32G. “It is unlikely that the form of packaging is necessarily proof that a substance is a particular drug.” Commonwealth v. Perez, ante 439, 444 n.4 (2010). Similarly, although the defendant was carrying a loaded weapon, a cellular telephone, and cash, these facts speak to the issue of distribution, not to the identity of the substance as heroin. See Commonwealth v. Vasquez, 456 Mass. at 366-367 (“Evidence seized . . . included a scale, rubber bands, a substantial amount of cash, sandwich bags, and a walkie-talkie — all relevant on the issue of distribution. But none of this properly admitted evidence established that the substances purchased and seized were ‘cocaine,’ as the indictments charged”).
Moreover, there was no direct evidence establishing the *669identity of the powder. See Commonwealth v. Fluellen, supra at 527. No field testing was performed. Contrast Commonwealth v. Connolly, 454 Mass. 808, 831 (2009). Nor did a police officer or other witness experienced with drug use opine that the substance was an illegal drug. See Vasquez, supra at 365; Pimentel, supra at 239. The only direct evidence of the composition of the seized substance was the drug certificate. In these circumstances, the admission in evidence of the drug certificate was not harmless beyond a reasonable doubt, and the defendant’s conviction on the drug charge must be reversed. See Vasquez, supra at 366.
b. Ballistics certificate. The ballistics certificate introduced at trial stated both that the gun seized from the defendant was test fired without malfunction and that the two magazines of bullets recovered from him (one in the gun he carried and the other in his coat pocket) were ammunition. Both the gun and the magazines were exhibits at trial. The Commonwealth also offered the testimony of the officer who recovered the gun and magazines from the defendant. In this respect, the facts of the instant case are very similar to those in Commonwealth v. Muniz, 456 Mass. 166 (2010).
As in Muniz, supra at 172, the admission of the ballistics certificate here was not harmless with respect to the defendant’s two firearm possession charges. In order for a gun to be a firearm for statutory purposes, it must be a weapon under a certain length that is operable, or capable of discharging a shot or bullet. See G. L. c. 140, § 121, as inserted by St. 1998, c. 180, § 8. See also Commonwealth v. Ware, ante 53, 56 (2009). The Commonwealth argues that the evidence that the .40 caliber gun found on the defendant was loaded, had its serial number scratched off, and was located at the defendant’s belt line near the small of his back, and that the defendant carried extra ammunition was overwhelming evidence that the gun was operable. We disagree.
We start with the fact that the defendant did not concede at trial that the gun was operable, see Commonwealth v. Brown, 75 Mass. App. Ct. 361, 363 (2009), nor was there any evidence that the gun had been fired. See Commonwealth v. Hollister, 75 Mass. App. Ct. at 732-733. Contrast Commonwealth v. Depina, 456 Mass. at 249 (“lawfully admitted evidence” that firearm was a working firearm overwhelming); Commonwealth v. Mendes, *67075 Mass. App. Ct. 390, 397 (2009) (“The strength of the independent evidence of the operability of the handgun shows beyond a reasonable doubt the harmlessness of the admission of the certificate. That independent evidence included testimony of three audible shots, the three empty casings, and the smell of gunpowder”); Commonwealth v. Pittman, post 905, 907 (2010) (“overwhelming evidence independent of the ballistics certificate that the gun in question was operable”). While the gun here was loaded, “a gun may be loaded and, at the same time, not capable of discharging a bullet due to a malfunction or misadjustment in the firing pin or some other part of the gun’s mechanism.” Hollister, supra at 733. “Thus, although the fact that the gun had ammunition in it bore on the question whether the gun was operable, it was not of such strength to conclude that the admission of the ballistics certificate did not contribute to the findings.” Ibid. See Commonwealth v. Muniz, 456 Mass. at 172.
In concluding that the admission of the ballistics certificate with respect to the two firearm possession charges was not harmless beyond a reasonable doubt, we further note that the Commonwealth referred to the certificate several times at trial, including in the prosecutor’s opening argument, during a witness’s testimony, and in closing argument. See Commonwealth v. Perez, supra at 444 (“[T]he Commonwealth’s reliance on the certificates was significant”). See also Commonwealth v. Loadholt, 456 Mass. 411, 433-434 (2010). The prosecutor also directly challenged defense counsel’s argument that the preparer of the certificate was not present to testify and underscored for the jury that the law permitted the use of a certificate as prima facie evidence even in the absence of the person who prepared it.
The fact that the ballistics certificate was consistent with the Commonwealth’s circumstantial evidence on the operability of the gun “does not mean those [certificates] were cumulative of otherwise properly admitted evidence.” Commonwealth v. Dagraca, 447 Mass. 546, 554 (2006) (emphasis in original). See Commonwealth v. Tyree, 455 Mass. at 701. See also Commonwealth v. Rosario, 430 Mass. 505, 511 (1999) (when determining whether an error was harmless, we examine whether the erroneously admitted evidence was cumulative of other evidence). The only direct evidence that the gun found on the defendant was capable of firing a shot or bullet was the ballistics certificate. *671Thus, although other evidence was before the jury, it was not so overwhelming that it rose to the level where we can say that the admission of the ballistics certificate did not contribute to the findings and was thus harmless beyond a reasonable doubt.
We turn now to the defendant’s conviction of unlawful possession of ammunition and conclude, pursuant to Muniz, supra at 172-173, that the admission of the ballistics certificate with respect to this charge was harmless beyond a reasonable doubt. The charge of unlawful possession of ammunition requires the Commonwealth to prove that the bullets found on the defendant were “designed for use in any firearm.” G. L. c. 140, § 121. Muniz, supra at 173. Here, as in Muniz, the Commonwealth introduced in evidence the gun, the magazines, and the testimony of an officer that the gun was loaded when discovered. See id. at 171. “The cartridges themselves and the officer’s testimony that they were found in the magazine, which was in the gun at the time it was seized, provide overwhelming evidence that the cartridges met the statutory definition of ammunition.” Id. at 173. See Commonwealth v. Loadholt, 456 Mass. at 434. Accordingly, we affirm the defendant’s conviction of unlawful possession of ammunition.
Conclusion. We cannot conclude that the ballistics and drug certificates did not contribute to three of the verdicts returned against the defendant. With respect to these, the admission of the certificates was not harmless beyond a reasonable doubt, and the defendant’s convictions of possession of a class A substance with intent to distribute, G. L. c. 94C, § 32(a); unlawful possession of a firearm, G. L. c. 269, § 10(a); and possession of a firearm with a defaced serial number, G. L. c. 269, § 11C, must be reversed and the verdicts set aside. The conviction of unlawful possession of ammunition, G. L. c. 269, § 10(h), however, is affirmed. The case is remanded for further proceedings consistent with this opinion.
So ordered.
The Commonwealth’s argument that the defendant did not preserve an objection on constitutional grounds to the admission of the certificates at trial is without merit. At trial, defense counsel objected to the admission of both the ballistics and drug certificates with sufficient specificity as to preserve the issue for appeal. See Commonwealth v. Depina, 456 Mass. 238, 248 n.8 (2010). In any event, in its recent decision, Commonwealth v. Vasquez, 456 Mass. 350, 356-359 (2010), the Supreme Judicial Court held that even unpreserved errors based on Melendez-Diaz are entitled to the more favorable standard of review. Thus, our review is pursuant to the harmless beyond a reasonable doubt standard.
The remaining Van Arsdall factors are “[1] the importance of the witness’ testimony in the prosecution’s case, [2] whether the testimony was cumulative, [3] the presence or absence of evidence corroborating or contradicting the testimony of the witness on material points, [and] [4] the extent of cross-examination otherwise permitted.” 475 U.S. at 684, citing Harrington, 395 U.S. at 254.