Yeppers, a billion and a half rounds that could be tracked...I'd bet there's at least half that number (and I'm being very conservative). By the way, that doesn't count reloading components.
At the RangeMaster Tactical conference, one of the biggest dinner conversation topics was how instructors were cutting down ammo requirements for training because the students either couldn't afford the training with the higher ammo component or simply couldn't get the ammo. Several of the instructors reported students coming through classes with .22 LRs, something they probably wouldn't have allowed in years past but now is completely acceptable.
I TOTALLY agree on this point — training is critically important, and I think training with a .22 is still good quality training. We've talked about this on SHOOTING GALLERY last season and repeatedly on DOWN RANGE Radio. At this point, I'm doing most of my own practice with .22s, and I'm pretty worried about the big chunks of ammo we use each season in the television shows. I've already started drawing on my own "strategic reserves" for the shows...I'm buying on a weekly basis, but there's just not that much out there.
So I strongly urge you to augment your basic personal defense battery with a "mirror" .22s for practice. Best cases are conversion units because you get 100% "look and feel" of your carry guns. You guys know I work with Tactical Solutions...the reason I do is they make the best .22 conversion units in the business, not to mention their superb Pac-Lite top ends for Rugers and Browning Buckmarks. For 1911s, I can also recommend Kimber .22 conversion units.
If you carry a snub revolver (and who of us doesn't at some point), take a look at this Charter Arms Pathfinder, 2-inch .22 LR snub with an MSRP of $379! I'm using my old Walther TPH .22 for BUG practice these days.
On rifle practice, conversion units are the best, but it's most important to match optics. Again, . I have a Tac-Sol unit fitted on a Stag lower and it is my main AR these days. The Black Dog mags are 100%. On your .22, as much it may simply be too expensive to go out and duplicate the optics. My "working" AR, an S&W M&P, is fitted with an Aimpoint M4 and 3X magnifier, which costs a tidy sum. The Tac-Sol .22 is fitted with an inexpensive BSA red dot, but it does the job and gives me the same red dot. Again, in full disclosure, BSA is a sponsor, but they've long been known for their great rimfire scopes. BTW, they have a reasonably priced fixed 4X coming out specifically designed for ARs...I've handled an advanced copy and like it. You don't need the top-of-the-line stuff on a .22, but you do need rimfire optics that match what you use on the working gun.
If money is tight (and it is), look at a 10/22. I didn't have to tell you that, right?