The photographic experts for the HSCA concluded that the rifle in the photos was the same rifle recovered by the Dallas Police.
Conclusions aren't evidence. You have to look at what the conclusions are based on. In this particular case, a single panel member, Cecil Kirk, saw what looked to him like a single mark on the forestock of the rifle in the CE133A photo, and the CE139 rifle also had a mark in the same general area. He said in his testimony that he thought that "tilted the scales" for it being the same rifle. No measurements were provided for the mark in the photo -- no data for it whatsoever. Lyndal Shaneyfelt saw the same mark in 1964 and (perhaps more honestly) said that it is not sufficient to warrant positive identification.