I had the opportunity to take two new AR-15 shooters to the range this week and an issue came up that likely affects many users of this rifle platform – proper implementation of back up iron sights (BUIS).
How many of you completely remove your red dot sight (RDS) when you zero your BUIS? I know I used to because it made it “easier.” Nobody wants to miss a chance to use that nifty quick detach (QD) mount that costs some extra hard earned dollars! If this is you, then you may want to try using your iron sights through the RDS to confirm your BZO (battle sight zero).
Having the RDS in place between the front and rear BUIS may change the way you see or index the sights and as a result the point of impact of your rounds may be off enough to notice at 50 yards. This is especially true if your Aimpoint/RDS is set with a “lower 1/3” co-witness mount. Lower 1/3 mounts place the optic slightly higher than the BUIS sight plane so that your view is less obstructed by the front sight. While I see this as a worthwhile benefit, it does make the BUIS a little more difficult to index, see, and use through the RDS.
This issue is mostly negated if you run an “absolute” co-witness optic mount. I personally don’t prefer these mounts because the front sight (I prefer a fixed front sight base on fighting ARs) is a little more intrusive on the “field of view.” I find that guys who typically don’t “trust” RDS tend to run the absolute co-witness mounts so that the irons are easier to use in an emergency.
Everything is a trade-off and I trust my RDS as much as any other high quality gear item I run on my rifles. Anything, no matter how expensive or tried and true, can fail at the worst possible moment and having multiple back up plans is always a good thing. So there you have it – a great reason to get you and your rifles out to the range to test and make sure everything is adjusted appropriately.
I usually zero in my iron sights first at 50 yards. I shoot at 7″ bowls that have a 5″ bottom. The front sight covers nearly the entire plate from side to side. The sight picture with just the iron sights, just a small crescent of the bowl is visible at the top of the sight. With the type of mount I use with my EOTech (a GGG mount), the 1MOA red dot sits just on top of the front sight. The sight picture I have with the red dot is in the center of the bowl.