They tried a meat bullet don't think they got it working either. In the movie it was never supposed to work the person firing the ice bullet was being setup his target set the whole thing up to arrange for someone else to be killed and the sniper with the ice bullet would take the blame.

Using a co gun should work. I have an umarex and that thing hits hard, and it's possible an ice bullet may penetrate, but it depends where it's shot at.

I feel like the article you linked doesn't support your conclusion, at least for the technique described in the article as an improvement over what people were doing before 2013. Those NIST researchers seemed to conclude that their 3D scan techniques can reduce the false positive rate to very low numbers, even when comparing 9mm rounds fired from consecutively manufactured handguns of the same model. At least if they recover an undamaged bullet that didn't get mangled by the actual shooting.

But yeah, the previous method sounds about as reliable as the My Cousin Vinny expert testimony: maybe getting things down to a range of possible models, but not specifically identifying a specific gun.

Now I kinda wish I had a mythbusters budget for comparing bullet and casing markings to both replicate the NIST study and to just compare whether different manufacturers have very different markings for the same caliber.

I wonder if it's something that used to work when guns were less consistently mass-produced

Or maybe it's always been nonsense, never knew that though thanks