I was in Cabela's today buying a new belt--a real belt, something stiff enough to handle a proper handgun in a concealment holster, and likely to last a while. (I bought a dress belt at Target a couple months back, because my old belt had become too long--what a tragedy--but it didn't last very long. It literally broke where the buckle grabbed the leather.) While there, I found myself staring at the Cabela's brand .22 to .50 caliber laser bore sighter. For $49.95, I couldn't turn it down. This is "Proudly Made in the U.S.A." by LaserLyte.
If you don't know what a laser bore sighter is--I guess that I better explain. You really would like to know that your riflescope or iron sights are aligned with the point of aim of your bullets. You don't know for sure until you actually fire some rounds--but it is darn frustrating, especially if you have a new scope (as I do for one of my rifles), to get to the range, fire a couple of shots, and not see them on the paper.
Before lasers, you could take your rifle far enough apart to stare down the barrel, and see where the barrel seemed to be pointing. You could look through the scope, and see where the crosshairs were pointed. Assuming that you had the barrel and scope combination properly clamped in position, you could then adjust the reticle on the scope until it was coincident at 25 meters with the view through the barrel. It doesn't sound particularly pleasant, but at least you were close enough to being on target that the first shot at the range might be within a few inches of the right spot.
Lasers changed everything. There are laser bore sighters that look just like a cartridge, and go into the chamber of your gun. They project a laser beam out, and you can then look through the scope (or iron sights) see if they are pointing to the little red dot. These are specific to a particular cartridge, of course, so if you have more than one caliber, you need one for each. The price adds up pretty quick.
What I bought is a multipurpose device. It consists of a laser in a tapered aluminum housing with a series of different arbors that you screw into one end. One arbor covers the range .220 - .270, another .280 to .349, another .350 to .434, and finally, .435 to .50. Depending how tightly you tighten the screw, you get in that range of calibers. You slide the end with the arbor into the muzzle end of the barrel, and turn it on. It now projects a red dot at the location where your barrel points.
Because most rifles are set up to slightly aim up, the bullet's trajectory typically cross the aim point at 25 meters and again (falling) at 250 or 300 meters. Find a target at 25 meters, turn on the laser, and then adjust your iron sights or scope reticle so that the aimpoint coincides with the laser dot. It isn't going to be perfect--but close enough that when you go to the range, you won't be far off.
UPDATE: Since the laser isn't bright enough to see in bright sunlight at 25 meters, the following calculator may be useful for figuring closer distances (such as in your garage).
UPDATE 2: I spent a bit of time remembering how the iron sights on an AR-15 work with the standard ball ammo trajectory, and I have some confidence that I am at least going to be on the paper at 100 meters, and perhaps even 300 meters. (My, it has been a long time since I shot this rifle.) The M16A2 sights that the AR-15 uses have an adjustment dial that moves the rear sight up with markings for 300, 400, 500, 600, and 700 meters. I am skeptical that this feature gets used in combat very often, partly because the numbers are hard to read (embossed in the metal, and you have to look from the side to see them), and because at 500 meters and beyond, if you don't have a laser range finder, you are close to guessing how far away your target is. (There's a mechanism using the relative height of a man and the front sight post, but how often do you get someone standing at that distance to use for calibration?)
I also decided to see how the scope on the Ruger 10/22 was aligned as well. This is a somewhat less critical matter, because a 10/22 is primarily a 100 yard rifle because .22LR loses what little energy it has so quickly. I do not know if I have ever adjusted the scope on this rifle; it had a 3x-9x40mm scope when I bought it used. It has always shot reasonably well where I was pointing it, but it was mostly a plinker, anyway. I can immediately see, because of the bore sighter, that the scope needed adjustment to the left a bit, although vertical aim seemed pretty darn good--consistent with my experience shooting it.
I may even drive over to the BLM land a mile or so from the house a little later today and see how well the bore sighter works out with real shooting.