Has a counter expert in ballistics verified this?
At first I thought that that was a puzzling aspect of the case. I just thought why don't they get a ballistics expert to state categorically that the cartridges which allegedly match do not match. But as you know things are not so simple. Such testimony might well be inadmissible on some technicality.
All the same I think that it would be worthwhile to try to establish the truth by consulting expert witnesses. Diane Downs has few supporters and few experts would want to get involved. It would be smart to show the evidence to a canadian ballistics expert with no axe to grind rather than some guy who works in in Oregon, USA and who wants to keep on working there.
The are indications that shills for the prosecution know that the cartridges did not match. It is notable that there has never been a counter argument put in support Hugi and Murdock on that issue. If that evidence were genuine they could easily make supporters of Diane shut up. If it was genuine it would indeed be conclusive proof of guilt. But it was a lie, so they think it's better just to keep on repeating the lie.