D was tried on charges relating to the shooting of his girlfriend's cousin. The indictments charged three counts: armed assault with intent to murder; assault and battery by means of a dangerous weapon; and unlawful possession of a firearm. The 'firearm' charge required proof that the weapon had a barrel 'less than 16 inches' in length. The victim testified at trial that D had shot him with 'a pistol,' specifically 'a revolver' that 'appeared to be a .32 or a .38.' The prosecution introduced no other evidence about the firearm. D moved for a required finding of not guilty on the firearm count. The trial judge granted the motion, reasoning that there was 'not a scintilla of evidence' that D had possessed a weapon with a barrel length of less than 16 inches. The defense case then proceeded. D's codefendant presented one witness, and both defendants then rested. After a short recess, the prosecutor brought to the court's attention a Massachusetts precedent under which the victim's testimony about the kind of gun sufficed to establish that the barrel was shorter than 16 inches. P requested that the court defer ruling on the sufficiency of the evidence until after the jury verdict. The judge agreed, announcing orally that she was 'reversing' her previous ruling and allowing the firearm-possession count to go to the jury. D was convicted on all three counts. D then submitted to a bench trial on an additional repeat-offender element of the firearm-possession charge; the judge found him guilty. The Appeals Court of Massachusetts affirmed, holding that the Double Jeopardy Clause was not implicated because the trial judge's correction of her ruling had not subjected D to a second prosecution or proceeding. It rejected D's argument that the trial judge's initial ruling was final because Massachusetts Rule of Criminal Procedure 25(a) required the judge to decide D's motion when it was made, without reserving decision; the court reasoned that the Rule does not preclude the judge from reconsidering. The Supreme Judicial Court of Massachusetts denied further appellate review. The Supreme Court granted certiorari.