Guns: Close-Range Optics Failure Sighting for the AR carbine
Like a lot of gunbloggers, I use the AR-15 as my home defense gun. It's relatively easy to handle, hits harder than almost any pistol, and is more precise than a twelve-gauge shotgun, especially when firing at anything more than across-the-hallway distances. My AR also has one of those nifty red dot scopes mounted on it (an Aimpoint Micro T1 - I'll do a review in the future). Operation couldn't be simpler - put the dot on the target, pull the trigger, bullet goes where the red dot was. It's an incredibly fast way to hit things at close range, since you can keep both eyes open and focused on the target, instead of on a front sight.
Of course, that all goes out the window if the red dot disappears. Whether it's battery failure, a circuitry SNAFU, or just plain old bad luck, you can't assume that your close-range optic will be operational when criminals are breaking down your door...
So, you'll need to test your point-of-aims/point-of-impacts at a range with the optics off. There's no real substitute for this - with all the variances in ammo velocity/weight, sights, and mounts nowadays, you won't be able to consult a table that shows you where you should be hitting in close. The above target was shot at 7 yards with superslow PMC Bronze .223 out of my 16" M4gery - YMMV. Here's a brief explanation of the three close-range sighting techniques used:
Shooting Out of the Tube: This is the simplest, quickest method of close range sighting with an AR when your optic goes toes-up. You just center the bad guy in the field-of-view of your scope, and pull the trigger. You won't need to adjust your cheekweld at all, since in normal operation the red dot is roughly centered in the optic anyway. Two downsides: your gun will probably be hitting low at close range (assuming a typical 25 or 50 yard zero for the red dot), and minute changes in the relative positions of your eye, the scope, and your target can produce big variations.
Front Sight Centered in the Tube: This is almost as quick as shooting out of the tube, and it might work better depending on how your AR is set up. You use the scope as a giant aperture and center the front sight in it along with your target. This arrangement is a little more repeatable, and cants the gun sharply upward, which is sometimes necessary to counter the height-over-bore offset of the AR sights at close range.
Shooting Out of the Notch: If you have the misfortune of being forced to shoot at close targets for extended periods, you might consider "shooting out of the notch." With this technique, you ignore the aperture rear sight (some rear BUIS actually allow you to fold the aperture out of the way altogether) and use the U-shaped "notch" as a crude rear sight in conjunction with your front sight post. For most configurations, I've found this to be the most precise technique - it works particularly well for rifles with fixed BUIS, like mine. Shooting out of the notch cants the gun up slightly, too.