— Isaac L. Pam appeals his conviction at jury trial for first degree robbery while armed with a deadly weapon, and second degree assault while armed with a deadly weapon and a firearm. We affirm.
Pam was identified as one of two men who robbed a Schuck's Auto Supply store in Seattle on July 10, 1979. Four witnesses testified that one of the robbers carried a gun or shotgun. One witness recognized Pam because both he and Pam had been incarcerated in the King County jail at the same time. He called out to Pam, who pointed the weapon at him and warned him to "get away" before fleeing the scene. No shots were fired. The weapon fell apart as the robber was running away. Police recovered the wooden forestock of "what appeared to be a shotgun," as one officer testified. The remainder of the weapon was not introduced in evidence.
Pam first contends his conviction must be reversed because the trial judge failed to instruct the jury that the deadly weapon and firearm findings must be made beyond *473a reasonable doubt, as required by State v. Tongate, 93 Wn.2d 751, 613 P.2d 121 (1980). Pam neither requested appropriate instructions nor otherwise raised the issue at trial.
Our Supreme Court has not yet determined if this error may be raised for the first time on appeal, finding it unnecessary to reach the constitutional issue where failure to so instruct was harmless beyond a reasonable doubt. State v. Hall, 95 Wn.2d 536, 627 P.2d 101 (1981); State v. Claborn, 95 Wn.2d 629, 628 P.2d 467 (1981). We are likewise persuaded the error here was harmless beyond a reasonable doubt.
The State must prove, beyond a reasonable doubt, the existence of facts which increase a defendant's penalty. State v. Tongate, supra. Thus, the State must prove the presence of a deadly weapon in fact in order to permit a special finding that the defendant was armed with a deadly weapon under RCW 9.95.040. A defendant cannot be so found if the evidence establishes only that he was armed with a gun-like, but nondeadly, object. State v. Tongate, supra. Under RCW 9.41.025, the State must prove the presence of a firearm, i.e., "a weapon from which a projectile may be fired by an explosive such as gun powder." WPIC 2.10. The statute applies even though the weapon was not loaded at the time of the incident. State v. Hattori, 19 Wn. App. 74, 573 P.2d 829 (1978). But a gun-like object incapable of being fired is not a "firearm."
Here, four eyewitnesses testified that Pam was armed with a gun or shotgun. One witness testified that the robber pointed a shotgun at him and warned him to "get away." The sole issue raised by Pam's defense was the identity of the robber. No controverting evidence was offered which might support an inference that Pam carried only a gun-like object. As in State v. Claborn, supra at 633, "There is absolutely no evidence [that the defendant was not so armed], and this was never a contested issue at trial." A reasonable doubt is a doubt for which a reason based upon the evidence exists. State v. Tanzymore, 54 *474Wn.2d 290, 340 P.2d 178 (1959); WPIC 4.01. There being no evidence which would support a reasonable doubt as to whether Pam was armed with a real gun, we conclude that the failure to specifically instruct on the State's burden of proof with respect to the special weapons verdicts was harmless error. State v. Hall, supra; State v. Claborn, supra.
The trial judge denied a motion in limine by Pam to exclude evidence of his prior convictions for impeachment purposes. As a result of this ruling, Pam elected not to testify. Pam first contends that the ruling violated ER 609. We do not agree.
ER 609(a) provides:
For the purpose of attacking the credibility of a witness, evidence that he has been convicted of a crime shall be admitted if elicited from him or established by public record during cross-examination but only if the crime (1) was punishable by death or imprisonment in excess of 1 year under the law under which he was convicted, and the court determines that the probative value of admitting this evidence outweighs its prejudicial effect to' the defendant, . . .
Determination of admissibility of evidence for impeachment purposes is a matter within the sound discretion of the trial judge, State v. Thompson, 95 Wn.2d 888, 632 P.2d 50 (1981); State v. Alexis, 95 Wn.2d 15, 621 P.2d 1269 (1980). The trial judge's determination will not be reversed absent a clear showing of abuse of discretion. State v. Thompson, supra.
Here, the trial judge was aware that the probative value of the evidence must be weighed against prejudicial effect under ER 609(a). Neither the robbery nor the narcotics conviction entailed acts of violence, short temper, or combative nature as to which the prejudicial effect would most likely outweigh any probative value for credibility. Neither type of conviction is unrelated to the defendant's capacity for truth and veracity. Moreover, both parties emphasized the importance of Pam's testimony and the likelihood that his testimony would be the only exculpatory evidence *475offered. As our Supreme Court has stated, the foremost factor in weighing probative value against prejudicial effect
is a comparison of the importance that the jury hear the defendant's account of events with the importance that it know of his prior conviction. . . .
(Citations omitted.) State v. Thompson, supra at 891, quoting State v. Alexis, supra at 19. The trial judge concluded that, given the importance of Pam's credibility as a witness, the probative value of these convictions exceeded the potential prejudice to Pam. The trial judge neither fashioned a per se rule favoring the admission of such evidence nor abused his discretion in balancing the probative value of the convictions against their prejudicial effect.
Pam also contends the ruling was erroneous because it permitted the State to offer evidence of prior convictions for impeachment purposes where such convictions were not proven by the State to be constitutionally valid. We do not agree.
Unlike State v. Holsworth, 93 Wn.2d 148, 607 P.2d 845 (1980), upon which Pam relies, the allegedly invalid convictions were not sought to be used to establish an element of the offense. Rather, the convictions were directed toward impeaching Pam if he testified. Consequently, "the validity of the guilty plea upon which the conviction was based goes to a purely collateral matter; that is, the credibility of the witness." State v. Thompson, supra at 895. A conviction based upon a counseled guilty plea is prima facie reliable for impeachment purposes. State v. Thompson, supra.
Here, Pam was represented by counsel when he pleaded guilty to forgery in 1969 and to violation of the Uniform Controlled Substances Act in 1974. There is no contention that his 1968 robbery conviction was constitutionally invalid. These convictions were thus prima facie reliable and could be used for impeachment purposes. State v. Thompson, supra.
If Pam desired to prevent the use of these convictions for impeachment purposes, it was his burden to *476establish the existence of facts sufficient to show that a constitutional violation occurred which bears upon the reliability of the conviction. State v. Roland, 379 So. 2d 721 (La. 1979); State v. Vincent, 35 N.C. App. 369, 241 S.E.2d 390 (1978); Clayton v. Haynes, 517 F.2d 577 (4th Cir. 1975); Potts v. Estelle, 529 F.2d 450 (5th Cir. 1976). Because there was no evidence affirmatively showing that the challenged convictions are constitutionally invalid, and because their prima facie reliability is established by the presence of counsel, we conclude the trial judge did not err in denying the motion in limine.
Pam next contends the trial judge erred in allowing an eyewitness to testify that he recognized Pam because they had been incarcerated in the King County jail at the same time. Pam argues that the prejudicial effect of this evidence of other crimes, wrongs, or acts substantially outweighed its probative value and was therefore inadmissible under ER 403. We do not agree.
Evidence of other crimes, wrongs, or acts is not admissible to prove the character of a person in order to show that he acted in conformity therewith. It may, however, be admissible for other purposes, such as . . . identity,
ER 404(b). Such evidence may be necessary to make the testimony understandable to the jury. See generally 2 J. Weinstein & M. Berger, Evidence ¶ 404[15] (1980). If such evidence is relevant to show identity, it is admissible if its probative value is greater than the likelihood of unfair prejudice. ER 403; State v. Reed, 25 Wn. App. 46, 604 P.2d 1330 (1979); State v. Whalon, 1 Wn. App. 785, 464 P.2d 730 (1970). This is a question for the sound discretion of the trial judge. State v. Messinger, 8 Wn. App. 829, 509 P.2d 382 (1973).
Here, identity of the armed robber was the principal issue at trial. The eyewitness did not identify Pam when he was first shown a photo montage. He testified that he recognized Pam's picture but was reluctant to involve himself because he had been in jail and in the penitentiary and he *477did not want to be labeled a "snitch." He recognized Pam because he had seen him before in jail. Defense counsel cross-examined on the identification issue. The reliability of the eyewitness' identification was best understood in a context which adequately apprised the jury of the witness' opportunity to observe and the basis of his identification. The trial judge did not err.
We have considered Pam's remaining contentions. Each has, however, been resolved contrary to the position taken by Pam in controlling decisions of our Supreme Court and the Court of Appeals, and we consider additional discussion to be unnecessary.
The judgment and sentence are affirmed.
Durham, J., concurs.