Next question: what happens to the data that was collected on the guns that have been ruled out? Has it been destroyed, or is it now on a national database?.....
Unless you mean the forensic evidence of ballistic/barrel markings and primer indentations, it's already in the 4473 system, so there's not much to add. I believe the FBI maintains a database, but it's only for firearms collected as evidence in Federal matters.
And the usefulness of forensics as a
sole means of solving crimes is widely overblown in the public's mind, due to shows like
CSI:Hoboken, or whatever. It's very rare for forensics alone to identify the perpetrator. All it tells you is if the same person/gun was involved in a series of crimes, or makes the case in court more airtight once the perpetrator is found and they can then be compared back to the collected evidence. Actually figuring out who the hell did the crime is still almost always simple human intel, witnesses, beating the streets asking questions, or someone blabs.
The last high profile case where guns of certain makes/calibers were all rounded up for testing was the D.C. Sniper case. And we know how effective that was. Their Bushmaster XM-15 was stolen from a gunshop on the other end of the country. IMO, when they do this, it's more a sign of fishing/desperation because they have zero of the human intel that actualy cracks cases to go on, and there's a lot of media and political pressure to "look busy".
And the unconnected nature of random, thrill, and serial killers almost completely obviates the human intel chain, and that's why those types give law enforcment hives, and they've had to go to indirect methods like psychological profiling, and massive media coverage, so elderly mom starts to have doubts about her loner 40 y.o. son in the basment with his Barbie collection, and if the washing machine really did destroy all her pantyhose...
And the high profile gun case mentioned before that, the visits to everyone with a certain brand of aftermarket .380 ACP Makarov conversion barrel was because one was used in the murder of a Federal prosecutor or judge (I forget), and that kind of got Uncle Sam's dander up, and the FBI went into "no stone unturned" mode for several years over it.
And IIRC, unless it's the distinctive rectangular striker mark and primer flow into the Glock striker opening in the breechface, the only other commonly sold handgun with polygonal rifling is the HK family. And I believe the Glock and HK barrels do not have the same number of flats in them. (Or does it vary by caliber? IIRC, larger has more flats, smaller less .45 8 flats, 9mm has six?)
And while I don't know about Oklahoma or it's various jurisdictions, if I were planning something criminally minded here in SE WI and cared about my forensics trail,
a .40 Glock would be what I'd choose. Because it's the service sidearm of the MPD and I'm willing to bet the Glock 22 is the most widely used single make and caliber combination in the U.S. right now in LEO use...
