Not too long ago I discussed my decision to set up an absolute co-witness sight configuration on my BLK SBR project. As I learn more about the options it seemed like a good idea to also e plain the good and bad regarding the lower 1/3 configuration. Why bring it up now?
The lower 1/3 co-wit may not appear useful at first glance but there are many reasons why it is a pretty good idea. The theory behind the lower 1/3 is that your sight aperture is less cluttered and that gives the operator more vision. Look at the diagram below:
In the center portion of the diagram you can see how the red dot floating above the iron sights. Now imagine three or more threats in view. Keeping an eye on every threat and engaging becomes easier using the center option- there is less clutter obscuring those independent threats as you engage. This may not seem like a huge difference but in competition and in life-threatening defensive situations (think home invasion with multiple bad guys) this can make a life-saving difference.
Apparently I'm not alone- LaRue Tactical ( who has the most awesome tag line: 'Made in the dead center of Texas' – which is also where they are) is considered a leader in co-wit riser mounts. They offer a lower 1/3 option for almost every reflex sight– look at their optic combos for an example. However they don't offer an absolute co-wit riser for every optic. I ended up with an American Defense riser for my Trijicon relfex sight but I can tell you that it's much easier to find the lower 1/3 option out there.
One more reason why the lower 1/3 may be the place I end up at for my preferred system- Trainers like, Costa in Magpul Dynamics, tell you to aim low in CQB (as in base of front sight post low) to effectively use iron sights. The left side of the diagram above shows how you can end up with the same results by setting up the rear sight (set it high- like a 5 yd zero) on your cowitness to produce this effect. For more on what that simplifies check out this article on holdover and holdunder. That article makes home defense zero for long range and short range complex because his approach to sighting systems requires the operator to adjust for a short or long shot. The lower 1/3 cowitness makes it simple: dot or dot+irons.
There are lots of reasons to use both options- I prefer simple, no nonsense sight pictures. Using both eyes effectively may be enough to not need that 2/3 aperture view free of the clutter of a rear sight. Also I don't plan to use the rear sight all the time- that's why I got a flip-up. On the other hand using a lower 1/3 I get two ranges and one includes the absolute view- compelling, isn't it?
Anyway the answer to which is better lies out on a course of fire… For me anyhow. Also a 100yd shot in a home defense situation is unlikely for me at this point in time, so I should train like I will fight. Watch this space for updates as I learn the pros and cons firsthand.