Does red dot brightness (and bloom) change point of impact?

Does red dot brightness change point of impact?

Red dot/ reflex sights have taken over a large segment of the optical market.  Once plagued by battery life and durability issues, the red dot is has become ubiquitous.

I was first introduced to them in the mid-90s when I was in the Marine Corps.  I was working at the “range” (that is what we called the impact area) in the Marine Corps Air Ground Combat Center (MCAGCC) in 29 Palms, California, and was attached as a liaison to an Army SF unit.  They were running Aimpoint 3000s on their M4s, Mag 58s and M2s.   Outside of a couple visiting foreign units, these were the first reflex sights I personally saw in military use.  At the time my unit had M16A2s with IR lasers mounted to the standard round hand guard.  Daylight rifle engagements were strictly limited to iron sights.  I personally found the Aimpoint to be a game changer and became an early civilian adopter on my personally owned rifle (try shooting with iron sights from an M17 gas mask and it will make you a believer).

Red dot reflex sights are now proven technology.  I run a couple of different sighting systems on my ARs, but for my primary rifle it is iron sights and a Aimpoint Micro.  A year ago I wanted to get back to basics so I pulled the red dot off, threw it in my bag and ran straight irons (I shoot a lot with optics and wanted a break with the gas guns).  This weekend I put my Micro back on headed to the range (FYI, my Micro has been on its Larue mount bouncing around my range bag for the past year and it still held its zero)!

I’ve found running red dot sights at the dimmest possible settings tend to offer the greatest amount of precision and a sharper dot profile.  Too bright a setting and the dot becomes distracting and blooms out (appearing larger) into the target.  Finding an appropriate setting for the intensity of a red dot sight can be challenging in different lighting conditions.  Depending on the environment, a setting may be too bright in the dark and dim in the sun, alternatively when operating in low light conditions, the use of a white light requires a bright setting to be able to see the dot when it is activated. The last thing you want is the dot to wash out when you need it.

My buddy and I were shooting carbines with Aimpoint T1 and T2 sights over the weekend at 200 yards.  We both noticed a slight change in point of impact as dot intensity changed when we shot.  Do we think the dot moved? No. We suspected this is a function of the dot obscuring the target.

Take a look at the test target below, a QIT-99 Reversed (one of my favorite 0-300 yard targets).

I shot both four shot groups, prone, unsupported with Winchester M855 (really inaccurate crap) and a 16″ Daniel Defense barrel.  The bottom group was shot with the 2 MOA dot on a brighter setting (3 intervals up from where I picked it up).  The top group was shot with a dim dot aiming at the head (note you can’t see the inside box from the 200 yard line without magnification).  Note the slight (and arguably negligible) shift in POI (approximately 1.5 MOA horizontally).

We noticed this slight “shift” due to light intensity throughout the afternoon.  I began searching around and found this post on JPs website that talks about a preference for a dimmer dot because of the more refined shape.

I also reached out to a couple of notable shooters, all of whom had mixed experience with this.  One of the Army Marksmanship Unit (AMU) guys I spoke with pointed out that if you don’t shoot with the center of the dot you’ll have a POI shift. I happen to use the top of the dot, since I’ve found this provides more precision.

I realize most shooters are engaging targets at shorter distances with their red dots, but have you noticed bloom affecting POI in your shooting?  Let me know what you think on our Facebook page…