Iron sights have been part of shooting since the very least April 19th 1775. Aiming was a major part of our tactics that helped defeat the British unaimed volley fire. This being said, it should come as no surprise that we have learned, used, and lost uses for iron sights in all environments from jungles, deserts and even the frozen landscapes of Siberia. I am going to talk about a few of those techniques here.
First anyone ever wonder why there are 2 apertures on the M16/AR15 platform? Most people have looked and wondered but never cared. Some wondered then tried switching between the two and found no gain from it. There is a reason for it but first we need to talk about sight alignment.
TC 3-22.9 states “sight alignment is the relationship between the aiming device and the firer’s eye. To achieve proper and effective aim, the focus of the firer’s eye needs to be on the front sight post or reticle. The Soldier must maintain sight alignment throughout the aiming process.” It goes on to say for iron sights it is the “the relationship between the front sight post, rear sight aperture, and the firer’s eye. The firer aligns the tip of the front sight post in the center of the rear aperture and his/or her eye. The firer will maintain focus on the front sight post, simultaneously centering it in the rear aperture” To show how important sight alignment really is I will pull from FM 23-9 1974 which states “any movement the firer makes during firing that moves the relationship of the front and rear sights by one-tenth inch will cause him to miss a 300-meter target by 5 feet”
Now let’s get back to the different sized apertures. On the M16A1 the different sized apertures also had different elevations and zeros. FM 23-9 in the 1966, 1970 and 1974 versions stated “The aperture marked L is used for ranges from 300 to 500 meters, and the unmarked aperture for ranges from 0 to 300 meters” You zeroed at 25 meters using the L aperture and then switch back to the unmarked one which gave you a 250 meter zero. This sight was used for ALL targets below 300. The aperture was larger which allowed for greater error in sight alignment but made it very fast to use. In fact, using the large aperture is the Iron sight version of using a red dot sight. As long as you were looking through the rear sight and had the post centered, you would have acceptable sight alignment.
By acceptable I mean getting strikes at the most common ranges in combat since 1775 which are within 200 meters. The larger viewing area gave some distinct advantages during gunfights. Much like our red dots we maintained situational awareness, gained speed, and it was actually easier to focus on the front sight. The price for this was accuracy. In the balance of speed and accuracy the situation dictates the priority. Most military use a 19-20 inch wide target as a baseline. A 20 inch target at 200 is 10 MOA. This means at 25 my group could be over 2 and a half inches and still get hits at 200. At 100 that is a 20 MOA target. That means I could shoot a 5 inch group at 25 and get hits.
I lay this out because the speed that I gain is worth the lack of refined sight alignment at the ranges in which I will be working. I still have to have the best sight alignment as possible but I have room for error. If you have been paying attention to The Greats when they talk about shooting red dots they all have mentioned at some point mounting the rifle consistently and getting as centered on the sight as possible in order to mitigate things like parallax and sight alignment errors. This is oft used by those that advocate for learning irons before red dots also. The same argument applies to using the large or small aperture of the irons. For the M16A1/A2 user, the zero was conducted and train up for it using the smaller aperture, which built the consistency, then switching to the larger for actual use.
Today, most quality back up iron sights have a dual aperture for the same reasons laid out above. Most of the time, just like the 80s and 90s, the sight rides in the small aperture and never is switched to the large aperture. The reason why is lost knowledge. One of the goals of Primary and Secondary is education and that is the purpose of this article. Of note, the Army lost this knowledge too. If we hadn’t, we would probably would not have purchased a million poor quality BUIS that don’t have the dual aperture. Then again, we have a million rifles and eventually the primary sighting system will be an optic.
I will close by laying out a rifle zero and set up technique based on my perceived use.
Using the Army zero target (new version) zero iron sights using small aperture.
Open the offsets to the large aperture and confirm the ability to maintain groups using large aperture.
Conduct drills at 100 and 0-50 in order to learn holds for the irons.
Zero optic and conduct same drills as above.
Once you have your holds and set up your irons correctly you can, with practice, run irons just as fast as a red dot optic under daylight conditions. This has been tested and applied in two world wars and every war until the GWOT. It is still in use for most LE agencies and should be used by anyone with irons as their primary sighting system.
- Ash Hess