Why does it
need to specifically be one handgun a month? Why can it never be twelve handguns a year, say? After all, if the purpose of this kind of law is to impede the usefulness of straw purchasers--which it ostensibly is--limiting an individual to twelve guns over a twelve-month period should be equally effective as limiting them to one gun a month. Whereas it is quite possible for a private individual to find that his dealer or online distributor (e.g. Lipsey's
http://www.lipseys.com/ or Davidson's
http://www.galleryofguns.com/) is offering a special price on two particular models of handgun, both of which he's had his eye on for a while. Bear in mind that "handgun" includes .22-cal plinkers and target pistols, which are generally inexpensive (unless you're talking Olympic-grade; .22LR doesn't create a lot of pressure, so the metallurgy doesn't have to be of the same standard needed to shoot heavier calibers) and less than ideal for criminal applications. And hey, some people come into sufficient sums of money to buy two handguns from time to time, e.g. when they get their tax refunds, or an end-of-year bonus.
It seems to me that the whole "impeding straw purchasing" rationale is simply a fig leaf, and that the actual purpose of such laws is a) to harass legal gun owners and b) as a foot in the door for handgun registration; because how else are you going to ensure that someone isn't buying more than X guns within a given unit of time? Of course, proponents of such laws aren't going to tip their hand ahead of time and admit that registration will be next on the agenda. That will come only after the "one handgun a month" law comes into force, whereupon the proponents will say "gosh, I don't know why we didn't think of this before, but this law is unenforceable without a system of registration!"
I've witnessed this process in a different context. Sixteen years ago, I was a draftee brevet sergeant in the Dutch army, doing paperwork for two air force helicopter pilots functioning as liaison officers to the army's all new Airmobile Brigade. At the time, the air force was looking to buy attack helicopters, and the Ministry of Defense found itself pitted against the Ministry of Economic Affairs in attempting to convince parliament to approve the purchase of either American-made McDonnell-Douglas (since merged into Boeing) AH-64 Apaches, or French-made Eurocopter Tigres (so unproven that not even the French had bought any yet). One night while our section (S-3, Operations and Training) was having a friendly alcohol-fueled get-together, one of the air force officers explained the process. Basically, he said, what we want is AH-64Ds, but those are expensive; so we'll ask parliament to approve the purchase of the less sophisticated and thus cheaper AH-64As, and once we have those, we'll say "gosh, we could really increase our combat power if we got our A-versions upgraded to D-versions (or at least one out of every four helicopters), and it's not that much more money, much less than to switch to Tigres instead..."
It's essentially a variation on the "bait-and-switch" confidence trick.
And wanting gun owners to report lost or stolen weapons - oh, that's just so horribly evil that there's no hope for the guy.
The problem with seemingly "reasonable, common-sense" laws concerning guns is that they have all too frequently been subverted not to curb violent crime, but to impose de facto gun bans by making it too arduous for many private citizens to acquire and keep a firearm. In this case, the law is ostensibly intended to provide a way to nail straw purchasers, who buy guns on behalf of traffickers, and in the event a firearm recovered from a crime scene several states away gets traced to them, they say "oh yeah, a few months after I bought that gun, it was stolen out of my garage, but since there was no damage I could claim insurance on, I didn't bother to report it..."
The objection to this kind of law is that it doesn't contain, up front, a proposed means to distinguish a straw purchaser from a legitimate gun owner who genuinely lost a firearm, or had it stolen, without realizing it within the allotted time. The common problem with any law is that it's very difficult to predict how it could be abused until it comes into force, at which point it takes a major effort to get it repealed. By way of example, imagine if the "Patriot Act" hadn't come with sunset clauses. Who could have foreseen the massive abuse to which the provisions were put, right?