IF YOU WATCH NEWS FOOTAGE of our troops in Iraq and Afghanistan, you'll note that just about every single M16A2 rifle, M4 carbine, and even a lot of the light machine guns have red-dot sights. The Army now issues them, and some soldiers and Marines purchase them privately, because at close range, you can aim more quickly and hit more often with red dots than with iron sights or a scope. They make terrific sights for anyone who has to shoot fast, and fairly close, and who doesn't require a high degree of precision. This means most deer hunters.
The basic design works like this: The housing consists of a short 30mm tube. On its inside wall is affixed a red diode that projects a beam of light forward. When it reaches the front of the tube, the beam of light hits a thin, concave lens with a metallic coating that reflects red but lets all other colors pass through. So the red dot that you see is light from the diode coming back to you at the speed of...light.
Red dots, which are made by Aimpoint, BSA, Bushnell, and Truglo, do their voodoo by putting the dot and the target in the same optical plane, just as a scope does. But with a scope, you must also get your head on the stock in precisely the right place and then put the crosshairs where you want them. If you don't, the resulting parallax—the apparent movement of a reticle over a target that occurs when you move your head—means you won't send the bullet where the crosshairs are. Using a red dot, you hold your head in any position you please, just as long as you can see the dot, put the dot on what you want to hit, and shoot. More on parallax later.
Because eye relief is not a factor, you can install your red dot on the receiver, ahead of the receiver, or way out on the barrel.
Red dots are not nearly as precise as a scope. Part of this has to do with subtension, or the amount of target space the red dot covers. Most red-dot sights offer dots that subtend either 4 minutes of angle at 100 yards, or 3 or 2 minutes. I use 2-minute dots. They don't blot out the whole world and are easy to see in any kind of light.
Red-dot sights don't magnify (with the exception of the Leupold CQ/T, which gives you a choice of 1X–3X power).
THE BATTERY QUESTION
A friend of mine says, "I don't want to put my destiny in anything that uses batteries," and he is not alone. What could be more bloodcurdling than switching on your red dot and finding no dot? I think the problem is overrated. I've used red dots on my handguns since the mid '90s and never had a battery flameout.
Battery life on modern red dots is incredibly long. Most last at least 600 hours, and the Aimpoint Comp ML3 that I just bought for my SOCOM16 carbine (Springfield Armory's short-barreled version of the M14) gives 50,000 hours even at a high setting.
LOOK MA, NO PARALLAX
Manufacturers hype the red dot's immunity from parallax; supposedly, you can see the dot in any part of your field of view, and as long as it covers the target...you're covered.
I tested this with my Aimpoint, sighting on an 8-inch bull at 100 yards and shifting my head so that I was seeing the dot from 12, 3, 6, and 9 o'clock, right at the absolute edges of the field of view. And by cracky, I hit the bull every time. (I can't vouch for other models.) What this means is, if you have to shoot fast, you don't have to align the sights precisely, and you save yourself a little bit of time that could make the difference between a buck on the ground and a buck bounding away and out of your life.