This is just another of those stupid gun laws that ignorant politicians scheme up, to pandy to their voters by passing "feel good" legislation, without a care for how brain dead it really is, and how ultimately counterproductive it is.
Here's my understanding of it:
In some states, before any particular type of gun can be approved for sale by the state legislature, manufactuers are required to fire test rounds, and archive them by cross-referencing the serial number, before they are shipped for sale to states like NY and MD. This applies to EVERY gun that is shipped to that state for sale.
The "logic" behind this requirement is that each gun barrel and chamber has unique machining marks that will cause equally unique microscopic abrasions (a ballistic "fingerprint") not only on the bullet, but also on the shell casing, which would make it easier for law enforcement to track down the gun in the aftermath of a shooting by examining the spent brass at a crime scene, and backtracking the documents to retrace the origin and sales path of the gun.
For this 'smart' law, we purchasers are:
[*] Limited by some states to the types of guns we can chose to buy, because certain guns are not approved
[*] Charged more for the gun, because it costs more time, labor and internal costs to set up the logistics to support this requirement
Now, here comes the stupidity of the plan.
How much does a replacement barrel cost?
How long does it take to pick up brass?
How far does brass from a revolver travel?
Yet one more idiotic gun law that does NOTHING to protect the population, but does give the anti-gun lobby one more incremental step to outlawing civilian firearm ownership by regulating what we have access to, thereby ensuring that the bad guys win, and the good guys lose.