Maryland's law is a perfect example! It has cost the state millions, has cost gun makers and dealers an unknown but substantial amount and has yet to solve a single crime. 
I'm not speaking in defense of this law, by any stretch of the imagination but I must ask, where do you get your information about it costing Maryland millions? 
It all depends on what they do with the cases. Its plausible if they send every case to the lab and enter the information into a database in an attempt to be able to match them to ones found in crimes. It seems to me that is exactly the problem. If you have a single case that was found at the scene of a crime,maybe you can tell if it came from a particular gun that you suspect was used in a crime. It all depends on the situation and if the gun is leaving unique marks on the case,and how unique those marks are. From what I have a scientist with any integrity should not be willing to write "This cartridge came from this gun" except for unusual circumstances. (say,there is a chip out of the tip of the extractor that leaves an otherwise inexplicable and distinctive mark) What they SHOULD be saying is "This cartridge is consistent with the weapon used in the crime. Furthermore it has these unusual features,and they are also consistent with the weapon used." Thats the most such an analysis can tell you,but that's not what prosecutors and police want to hear. As such,we end up with those scientists that can be badgered or coerced into throwing their integrity in the trash and saying whatever their bosses want them to.
The problem with collecting a cartridge from each gun is,how do you catalog them in a way that is useful. One thing I dont get though is the panic and fear that the idea of cataloging this information creates. I see its wasteful and useless. But the fear that somehow this will be used against you is absurd. First,its pretty much useless. Second,while the chance of my gun matching a criminals is very real,the chance of ANYTHING else linking me to the crime is remote. The chance of the two together happening is damn near impossible. Its much more likely that I was driving the same kind of car as the criminal,resembled the criminal,and was near where the crime was and that my gun WONT match,and that instead of having to worry about a erroneous match being used to convict me,none of my guns will match.
This isn't going to really worry them at all however. After all,I have many guns,maybe I just tossed that one in the river or took the acetylene torch in my garage to it. In other words,there are thousands of far more plausible ways to be falsely accused of a crime than having your cartridge matched to a criminals. (has this ever happened?) In fact,my 1911 came with a fired cartridge. I bet now that I have fired a few thousand rounds through it,it wont match cartridges that I fire now. If your that paranoid though,take your new gun,and polish all the parts up and fire-lap the bore. Then you KNOW it wont match. That wont help you though. An over zealous prosecutor and someone in the lab who wants a promotion more than he values his integrity may well find that a cartridge fired from a Glock magically matches the ones fired from your 1911. That being the case,who cares if they have the real case from your gun,which no longer matches yours anyway. For that matter,who cares about micro-stamping,which does in fact leave a uniquely identifiable signature on the cases. From that,Im in no danger at all. The only thing that tells them is if Im stupid enough to commit a crime with such a gun without changing out or polishing off the end of the firing pin. A smart criminal would go buy a microstamped Glock. They would then go buy a new barrel,firing pin and extractor and use those. They would then swap all the original parts back in and keep the gun. That way if the police suspected them,they would take their gun and test it,and find that it was NOT the gun that was used in the crime.
Im against these things because they are pointless burdens on firearms manufacturers,becuase they make guns more expensive,and because its a pointless waste of government money. A single extra police officer on the streets will solve far more crimes than these measures ever will.
I think its a bad idea for a completely different reason. Its a waste of money,which was enacted by people who watch to much CSI.
Flash, in reality,the witnesses statements are some of the worst evidence you can get. I witnessed a shooting once. I could have sworn it was a automatic the guy had. My friend standing beside me said it was a revolver knew the make and model of the gun. He knew it becuase he owned one. He was probably right. I was almost certainly mistaken,but to this day I still remember that he was holding a stainless semiauto. What really happened of course was that I didnt really look too closely at the gun. I saw it and what I remember was simply that he had a gun. The rest I filled in when the police questioned me. Thats how memory works. You dont encode a bitmap image of every single thing you see. Your brain filters out what it thinks is important and throws out the rest.
There is a classic experiment that shows this. A man walks up to a bus stop with a portable radio. Someone then runs by and steals it. The people at the bus stop are then questioned as to what the radio looked like and what the thief looked like. Typically everyone gives widely differing answers. In fact,they will often not only screw major details like what color and size the radio was but even get facts like what race the thief was wrong.
