In Commonwealth v. Todd, 477 Pa. 529, 384 A.2d 1215 (Pa. 1978), the expert's testimony was insufficient to establish the gun's barrel length. In Todd the Commonwealth's expert testified the weapon used was "probably" a Smith and Wesson .38 caliber weapon but that he had "no idea" how long the gun's barrel might have been. The court held that absent any evidence indicating the gun's barrel length, the evidence was not sufficient to support appellant's firearms conviction.