I learned a lot of misinformation about guns while in the Marine Corps. Oddly, most of it was ‘unofficial’ knowledge that contrasted what the Marine Corps taught. One was the idea that our DM’s suppressor would wear out, so he should rarely use it. Our DM (Designated Marksman) had zeroed his rifle with the can and was now told to remove it until needed. He was the first to explain to me that it would affect his zero and point of aim. He was deeply annoyed.
This 1st Lt. was confident in his misinformation, which resulted in an ‘aye sir,’ and our DM strategically removed his suppressor when leaving and coming into the FOB. This introduced me to the idea of a zero shift with suppressors. Now, more than a decade and some change later, I decided I wanted to investigate the phenomenon and see why and how much shift occurs when you mount a can or remove it, depending on your zero and point of aim.
I hoped to have a definite answer, but sadly, the best I can come up with is, “It depends.”
How Suppressors Affect Point of Aim
When you shoot your rifle, your barrel doesn’t stay still. It might be fixed in every sense of the word, but when you fire, that barrel moves around a lot. You just can’t see it. You’ll have to watch a super slow-motion video to see it, but it’s kind of crazy. It flexes and whips around, and it’s the reason why you shouldn’t mount optics to most handguards.
The barrel’s movement and vibration are commonly called barrel harmonics. They’re consistent with your gun and ammo, and that’s why your zero remains your zero. However, when you start to add or reduce weight, your barrel harmonics change. Suppressors add weight and can cause your point of aim and point of impact to shift.
How much the addition or removal of a suppressor shifts depends on several factors.
Point of Aim Shift and Suppressors – The Factors
Barrel Length and Weight
The point of impact shift can be small or radical, and the barrel length and weight matter. Shorter and lighter barrels tend to have greater movement changes when shooting, while longer and heavier barrels tend to have a smaller point-of-aim impact.
Suppressor Weight
Suppressor weight is another factor. If you swap suppressors, you’ll notice a POI shift. A heavier suppressor creates a shift that’s a lot different than a lighter suppressor. Outside of swapping suppressors, it seems that heavier suppressors create a more pronounced POI change.
The Baffles
Baffles slow the burning of gasses down, which cools them and helps suppress the weapon. That action also shifts your point of impact. It’s an effect that’s tough to mitigate and even happens with other types of muzzle devices.
How Much Point of Aim Shift?
As established, it depends, but for fun, I took my only suppressed AR out and launched some lead. I originally zeroed the SAI 1-6X with the suppressor in place with a simple 50/200 zero. I returned to the 50-yard line and used a series of two-inch dots to test the difference between firing suppressed and firing unsuppressed.
My ammo was cheap 55 grain .223. I fired a five-shot group into the top middle two-inch circle so I could fire on the left and right bottom targets and observe for shift. I let the suppressor cool while checking my target. I popped it off the QD mount and fired another five-round group.
I aimed dead center as best I could, but the rounds all hit high. One hit to the right, but that was my fault, flyer. Outside the flyer, the second group was tighter. That’s because, between strings of fire, I added a pistol box to my range bag, which made it a sturdier rest than just the bag.
The group is a little over an inch off target, high at 50 yards, and represents about a 2.5 MOA shift high. That’s a decent little jump between the two groups, but you’d still hit your deer or threat.
Mitigation
The best mitigation would be to zero suppressed and keep the rifle suppressed. You can also experiment and learn whatever holdover is necessary to swap between the two. Since mine hit high, the easiest thing would be to aim a little high. However, if your point of impact shift is high and left or high and right, it gets more complicated.
Maybe suppressed rifles should just stay suppressed?
