You might check and see how the barrel for this revolver was made. Many Years ago I read that some Revolver and Pistol barrel were made in a longer length rifled then cut to the length to fit the intended revolver or pistol. In this process it would seem that several different weapons could have the same rifling impressions. Like I said this was many, many years ago that I read this. Whether this is true or not I do not know. Unless the prosecution can prove that your client fired the weapon in question. He cannot prove which weapon the bullet came from. There are literally 10s of million of 38 caliber revolvers.