The defendant raises two primary issues in this appeal from his convictions of various drug and firearm offenses.1 First, he argues that admission of certificates of drug and ballistics analysis, absent live testimony, violated his right to confrontation pursuant to the Sixth Amendment to the United States Constitution. Second, the defendant contends that evidence seized from his residence should have been suppressed for lack of probable cause. We reverse all but the ammunition conviction given the error in admitting the certificates. But because we conclude that there was probable cause to search the defendant’s residence, we remand for new trial on those charges.
1. Sixth Amendment. Ballistics and drug certificates were admitted at trial over the defendant’s objection. There is no doubt that their admission, absent live testimony or the opportunity to cross-examine, violated the confrontation clause of the Sixth Amendment. Melendez-Diaz v. Massachusetts, 129 S. Ct. 2527 (2009). We review, therefore, to determine whether the admission of the certificates was harmless beyond a reasonable doubt. “Our review presumes that the constitutional violation requires reversal, but an affirmative showing of harmlessness beyond a reasonable doubt by the Commonwealth will preserve the convictions.” Commonwealth v. Fluellen, 456 Mass. 517, 526 (2010). “In considering the essential question 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, our focus is not on whether the jury could have convicted the defendant had the tainted evidence been excluded; it is not *264enough for the Commonwealth to demonstrate that its other, properly admitted evidence was sufficient to convict the defendant or that the inadmissible evidence was consistent with the admissible evidence. Rather, 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) (quotations and citations omitted). See Chapman v. California, 386 U.S. 18, 23-24 (1967).
The Commonwealth primarily argues that the erroneous admission of the certificates was harmless beyond a reasonable doubt because neither the composition of the narcotics nor the operability of the firearms were “live” issues at trial. This, however, is not enough where, as here, there was little (if any) evidence to prove the nature of the substances or the operability of the firearms. See Commonwealth v. Vasquez, 456 Mass. 350, 368 (2010); Commonwealth v. Charles, 456 Mass. 378, 383 (2010). Even if a defendant does not contest the composition of the alleged drugs, or the operability of a firearm, the “defendant’s theory of his case cannot relieve the Commonwealth of its burden of proving every element of a crime beyond a reasonable doubt.” Commonwealth v. Shea, 398 Mass. 264, 269 (1986). Nor does the fact that defense counsel at various points referred to the objects as a “gun,” or heroin, or cocaine satisfy the Commonwealth’s burden of proving the guns’ operability or the substances’ composition.2 Commonwealth v. Charles, 456 Mass. at 383.
That said, we conclude based on Commonwealth v. Muniz, *265456 Mass. 166, 172-173 (2010), that the admission of the certificate of ballistics analysis with respect to the ammunition charge was harmless beyond a reasonable doubt. The crime of unlawful possession of ammunition requires the Commonwealth to show that the bullets found in the defendant’s firearm were “designed for use in any firearm.” G. L. c. 140, § 121. Here, as in Muniz, 456 Mass, at 171, the Commonwealth introduced in evidence the gun and the rounds found inside the gun when it was seized. A police officer testified at trial that the rounds were found inside the gun. “The cartridges themselves and the officer’s testimony that they were found ... in the gun at the time it was seized[] provide overwhelming evidence that the cartridges met the statutory definition of ammunition.” Id. at 173.
2. Motion to suppress. The defendant argues that the affidavit supporting the application for a search warrant did not set forth a “nexus” with his residence sufficient to establish probable cause. To determine whether a sufficient nexus has been made out, we read the affidavit as a whole, without isolating or deconstructing its individual parts, or subjecting it to strained or hypercritical analysis. See Commonwealth v. Blake, 413 Mass. 823, 827 (1992). “The nexus may be found in ‘the type of crime, the nature of the missing items, the extent of the suspect’s opportunity for concealment, and normal inferences as to where a criminal would be likely to hide’ the drugs he sells.” Commonwealth v. O’Day, 440 Mass. 296, 302 (2003), quoting from Commonwealth v. Cinelli, 389 Mass. 197, 213, cert, denied, 484 U.S. 860 (1983).
“When that location is a residence, there must be specific information in the affidavit, and reasonable inferences a magistrate may draw, to provide ‘a sufficient nexus between the defendant’s drug-selling activity and his residence to establish probable cause to search the residence.’ ” Commonwealth v. Pina, 453 Mass. 438, 440-441 (2009), quoting from Commonwealth v. O’Day, 440 Mass. at 304 (single observation of drug dealer leaving his residence to go to drug transaction did not provide sufficient nexus). “Information establishing that a person is guilty of a crime does not necessarily constitute probable cause to search the person’s residence.” Commonwealth v. *266Cinelli, 389 Mass. at 213. “It follows that probable cause to expect that drugs will be present in a home is not established by the fact that the defendant lives there.” Commonwealth v. Pina, 453 Mass, at 441. Just as residency alone does not establish probable cause, “the fact that a defendant drives from his home to the location of a drug transaction, and returns to his home on the transaction’s conclusion, with no other facts connecting the residence to drug sales, does not provide probable cause to search the residence” (emphasis added). Commonwealth v. Medina, 453 Mass. 1011, 1011 (2009), quoting from Commonwealth v. Pina, 453 Mass, at 441 (single round trip to and from drug transaction did not establish probable cause to search residence). Among the infinite variety of additional facts human behavior can provide (together with the reasonable inferences to be drawn from them) to establish probable cause to search a residence, one cannot exclude a drug dealer’s pattern of leaving and returning to his residence for each drug sale. A pattern of repeated activity giving rise to a reasonable inference that a dealer’s residence is being used as the base for his drug operation provides sufficient nexus to search his residence.
Summarized, the facts in the affidavit in this case were as follows. A confidential informant (Cl) told police that he (a pronoun used for convenience, not to signify gender) knew of a heroin dealer in Brockton who used two different automobiles (one a white Toyota, the other a green Audi with fancy wheels) to deliver drugs to prearranged locations. Using this information, the police worked with the Cl to make four controlled purchases of heroin over the next two weeks. On each of these occasions, the Cl called the defendant by telephone and asked for a specific quantity of drugs. The defendant then specified the location at which to meet. The defendant arrived by car (either the white Toyota or the green Audi) and picked up the CL He drove a short distance with the Cl in the car, during which a sale of heroin took place. The Cl was then let out of the car. After each of these sales, the defendant drove directly to his residence, and parked the car in the parking lot. He then entered the house through its rear entrance, located near the basement. In addition, on one of these occasions, police observed the defendant drive the Toyota away from his residence a few *267minutes after arranging a sale by telephone with the CL The defendant then drove directly to the prearranged location where he sold drugs to the CI.
On two additional occasions during the same two-week period, the defendant was observed to leave his residence, get directly into the Audi, and drive to a location where he picked up a woman, drove a short distance, and then dropped her off. He returned directly to his residence. This behavior was in all material respects identical to the defendant’s modus operand! in the controlled purchases and it takes no leap of imagination to infer that these too were drug transactions.3 See Commonwealth v. Santiago, 452 Mass. 573, 576 (2008), quoting from Commonwealth v. Jimenez, 438 Mass. 213, 218 (2002) (“affidavits in support of search warrants are to be approached with a view toward common sense, read in their entirety and with considerable latitude allowed for the drawing of inferences”). On the first of these two occasions, the defendant took counter measures while driving to ensure he was not followed. Also on this occasion, after parking the Audi when he returned home, he opened the driver’s door of the Toyota and then its hood. After looking around to ensure he was not being watched, he either took something from the engine compartment or placed something in it. He then went inside his residence, using the rear door.
In summary, the defendant was seen leaving and returning to his residence multiple times to what were either known drug sales or to encounters that could readily be inferred to be drug transactions. A pattern of activity such as this, in our view, provides sufficient nexus to a dealer’s residence to satisfy probable cause to search it. In addition, the defendant’s use of multiple cars makes it more likely that he stored drugs in his residence, rather than in the vehicles. Moreover, whatever the defendant was storing in the engine compartment of the Toyota, he had no need to access it on the way to a sale. Rather, that material was either deposited into the compartment after a sale or taken from the compartment into his house. Either way, it bolsters the inference that drugs were stored in the house, rather than in the vehicles. Furthermore, the defendant always used the rear *268entrance to the house, and the landlord confirmed that the occupants of the defendant’s apartment were the only people (in addition to the owner) who had access to the locked basement and a locked storage container that were located at the rear of the house.
The defendant’s motion to suppress was properly denied.
3. Other issues. We address briefly the other issues raised by the defendant. The judge correctly determined that the defendant did not have an objectively reasonable expectation of privacy in the basement to which the landlord also had full access. See Commonwealth v. Williams, 453 Mass. 203, 208-209 (2009) (and cases cited therein). Finally, there was no error in denying the defendant’s motion for a required finding of not guilty regarding the charges based on items discovered in the basement. The evidence, taken in the light most favorable to the Commonwealth, was sufficient to allow a jury to find, beyond a reasonable doubt, that the defendant had constructive possession over the items in the basement.
For the reasons set forth above, the defendant’s conviction of possession of ammunition (indictment no. 06-00182-003) is affirmed. The judgments on the other indictments are reversed, the verdicts are set aside, and the cases are remanded to the Superior Court for a new trial.
So ordered.
The defendant was convicted of trafficking in heroin (G. L. c. 94C, § 32E[c]); doing so in a school zone (G. L. c. 94C, § 32J); distributing cocaine (G. L. c. 94C, § 32A[c]); doing so in a school zone (G. L. c. 94C, § 32J); two counts of possession of a firearm or ammunition without a firearm identification (FED) card (subsequent offense) (G. L. c. 269, § 10[A]); and one count of possession of ammunition without an FID card (G. L. c. 269, § 10[/z]).
The Commonwealth’s evidence was not of such strength that the admission of the certificates was harmless beyond a reasonable doubt. As to the guns, while there was evidence that one of the guns was loaded, there was no evidence that it had actually been fired. See Commonwealth v. Hollister, 75 Mass. App. Ct. 729, 732-733 (2009). Contrast Commonwealth v. Mendes, 75 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”). As to the drugs, there was no expert testimony as to their composition, there was no field testing, and there was no other direct evidence as to composition.
It was also completely consistent with the defendant’s modus operandi as described by the CI when he first met with police.