Silencers 101

Suppressors and POI (Point of Impact) Shift

Suppressors and POI (Point of Impact) Shift

One of the more common terms you may see when it comes to rifle suppressors is POI shift. This refers to a change in the point-of-impact when adding or removing a silencer from your firearm and it can affect pistols as well as rifles.

There can be nothing more frustrating than having your firearm zeroed for a certain range with a certain ammunition type only to find it completely off in a different direction or even a different group size within a week.

No, it is not always shooter error. There are a lot of variables at work and any one of them can cause this to happen. The cause of POI shift with a suppressor can be one that is environmental, ammunition dependent, equipment failure, or by using a suppressor incorrectly.

What Causes POI Shift?

The primary culprit of POI shift with a suppressor and even without one often comes down to barrel harmonics. This is the way in which a rifle barrel moves and vibrates while the bullet is traveling down the lands and grooves to the bore. A firearm barrel may flex and distort greatly to the point where some shooters will refer to it as a whipping effect. Most often the vibration is not visible to the human eye but it can be observed through a high-speed camera.

After the projectile has left the barrel, it may still be vibrating like a tuning fork. This is most common in long and thin barreled hunting rifles. Those two features are what affect barrel harmonics and POI shift the most because those characteristics keep the barrel from returning to its baseline or neutral position to center. When the barrel is neutral, the POI will be repeatable due to the neutral harmonics.

We like to compare it to a guitar string being plucked and returning to its original position. This is how the barrel on your firearm behaves during the firing sequence. Thicker and heavier barrels are not as prone to POI shift by nature because those characteristics are closer to the baseline. There is still vibration, distortion, heat, and torque but there is a much quicker recovery time between shots. Likewise, short barrels are less affected than long ones because there is less travel of a projectile through a 4” pistol or 10” SBR (short-barrel rifle) than there is through a precision or hunting rifle with a 26” barrel.

In the old days shooters and gunsmiths sought to tame POI shift by bedding barrels and actions to stocks. However, this was found in many cases to exacerbate the problem. The solution was to bed the action and free float the barrel so that nothing touched it. In time, manufacturers applied this to the AR-15 platform by eliminating the front sight post and having the barrel surrounded by a rail type of handguard to allow the barrel to vibrate and return to neutral in its own time.

Hunters and snipers also take the time to ensure no foreign debris has made its way into the channel between the barrel and the stock. A twig, rock, dirt clod, or anything else can make contact with the barrel and cause a shift in POI by directly affecting the barrel harmonics.

Weather can also cause POI shift. It may not be as noticeable at short ranges less than 200 yards, but it is definitely a factor at 500 yards and beyond. There are many variables at play that become noticeable at longer ranges such as barometric pressure, precipitation, humidity, and altitude.

Another culprit for POI shift can be your ammunition. Different bullet weights will have different points of impact as well as ammunition made by different manufacturers. Loading data probably plays the biggest role with regard to POI shift than any other variable we have mentioned so far.

How POI Shift is Impacted by Suppressors

When it comes to suppressors, the biggest culprit for POI shift comes into play when zeroing a rifle with a suppressor and shooting it unsuppressed or vice versa. Most suppressors regardless of how light they are will cause a shift in POI because the weight will affect a barrels return to neutral.

The quick and easy way to resolve POI shift with a suppressor is to leave the suppressor mounted once the rifle is zeroed. However, this is not always practical or even possible. A mounted silencer may not fit in a rifle’s carrying case or a safe. There are times when the suppressor may need to be removed for cleaning or servicing either the rifle or the silencer. Other instances can involve the shooter having to take the rifle into a jurisdiction that does not allow suppressors or suppressed shooting. Lastly, the shooter may have one silencer and many different hosts.

A smart shooter will make notes of where the rifle shoots with a suppressor and without it and keep this information in a data book or even on a note taped to the rifle’s stock and make the necessary scope adjustments based on the status of the rifle.

However, there is another factor that affects POI shift, and that is how the silencer is mounted.

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How a Suppressor is Mounted Affects POI Shift

Suppressors that use a direct thread mount like the BANISH 30 are the least affected with POI shift. That is because the suppressor indexes at the same point when mounted and remounted every time. The baffles stay aligned with the same reference consistently. This may not be 100% but if an adjustment is needed on the optic or iron sights it tends to be minimal.

The second, less affected category is suppressors, which use a threaded muzzle brake or flash hider mount where the silencer does not thread onto the bare barrel threads but threads onto the outside of the muzzle device itself. Like a threaded barrel, it is not 100%, but POI shift with a suppressor is very minimal if it does happen.

POI shift with a suppressor is most notable when using a QD or quick detach type of muzzle device. Some of the worst offenders are those which use a ratcheting type mount where the silencer’s end cap has teeth that lock up against the muzzle device. This is a reason why many manufacturers are moving toward a tapered shoulder type of mount as opposed to a ratchet. The main flaw in the design is that the suppressor may not engage the same point every time when tightened due to carbon or other debris causing external fouling.

Another area of concern with any suppressor is that they can loosen up after firing. When this happens there is not only the risk of POI shift – although that is usually the first sign that the silencer is working itself loose – but also of the suppressor launching downrange when turning too loose. This is a reason why most suppressors used by the military and bought under contract have a secondary external lock as part of the requirements during the procurement phase.

It may seem silly to say this, but always check the suppressor, the mount, and the threads for carbon or other debris that may be preventing that positive repeatable lockup.

Weight plays a role in POI shift with a suppressor, which is the main reason why many shooters tend to prize a lighter weight can over a heavier one.

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Adjusting Your POI

While we have been primarily focused on POI shift and rifle suppressors it can affect your pistol as well. Luckily on a pistol silencer such as the BANISH 45, you have a built-in method of adjusting your POI on the fly.

If you are using the interchangeable spring-loaded pistons and notice that you are hitting in a different spot than you were previously, you simply grab the body of the silencer and pull it forward in the direction of the muzzle, rotate it and let it snap back into place.

What is usually happening with a pistol suppressor is that the baffle stack is not aligned exactly the way that it was prior. Some shooters will mark or otherwise make note of what position the suppressor is in when mounted to the pistol and after tightening will index to that same point via the method we described in the previous paragraph.

You cannot use this same method when employing the fixed barrel spacer on the BANISH 45 if you are using it on a carbine or pistol that employs a fixed barrel. In those instances, you must adjust optics or compensate by using Kentucky windage and or elevation.

Managing POI Shift

Remember, POI shift can and will occur when there is any change made to a barrel and that includes mounting or dismounting a suppressor. However, harmonics are repeatable and slight adjustments can be made to bring you back to zero. Suppressors like the BANISH 30, which is a direct thread silencer and the BANISH 45 which makes use of a spring-loaded piston system can minimize this occurrence but be mindful that it can still happen to such great designs as these and if you are going on a hunt or to a competitive shooting match, always recheck your zero before you go hot.

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