Boresighting off a sandbag is the quickest way to dial in your AR-15
Mounting an optic on an AR-15 is a simple affair, but getting it zeroed can turn into an adventure. AR-15 parts come from a wide variety of sources and once assembled into a rifle, it’s difficult to predict where the bullets will go when they leave the muzzle. I’ve seen shooters deal with this uncertainty by pulling the target board to distances as close at 10 yards to zero. That can be difficult to do on a public range. Here’s how to boresight an AR before firing even the first round and how to zero as painlessly as possible.
How to Bore-sight an AR-15
The AR-15 is a rifle designed to boresight. Don’t worry about all the gizmos and trinkets out there for bore-sighting. None of them are necessary to use with an AR-15 and just make the process take longer. The first step is to separate the upper receiver group from the lower receiver group by pushing the takedown and pivot pins aside and then pulling the two groups apart. Step two is to remove the bolt carrier group from the upper receiver and then place the upper with the optic mounted on it on top of a large shooting bag.
Set a Target Board at 50 or 100 Yards
Look through the back of the receiver and down the barrel. Move the upper receiver until the bore aligns with one corner of the target board. The bag should support the upper receiver so that it doesn’t move when released. Without touching the upper receiver, look through the optic and note where it is sighted in relation to the chosen corner of the target board. Use one hand to hold the upper stationary and use the other the adjust the optic dials until the optic is sighted in on the same corner as the bore. I usually repeat this process a couple times to ensure the optic and bore are closely aligned to the same corner.
Take a Shot
Put the rifle back together and load the rifle. Aim at the center of the target and fire one round. Ninety percent of the time I’ll be on the target board at 100 yards. If it’s a clean miss, I’ll fire one round at the top of the board and look for an impact. If that’s a miss, I’ll repeat the process by moving to the bottom and then left and right sides of the target board and firing one round at each stop while inspecting for impact between each shot. If all of those are misses, I begin the process of bore-sighting once again. It’s unusual to have to repeat the bore-sighting process a second time.
I prefer this process to using a boresighter because it is faster, especially after a shooter has done it a few times.
Notes on Various AR-15 Optics
Of all the optics to zero on an AR, magnified optics are the easiest because they offer the most precise point of aim and clearest view of the target board’s corner. Red dots are harder to zero but turning down the dot’s brightness until it is just barely visible makes it small and clearly defined because it eliminates blooming. Turning down the dot’s brightness makes it easier to zero. Finally, a range bag makes a good base from which to zero an AR-15 upper receiver group. Range bags are usually wide and offer a lot of surface area to help stabilize the upper receiver. A close second would be a large rear bag with the upper sitting on a bipod. One hand can easily secure the rifle and hold the rear bag while the other moves the optic’s point of aim.