POI shift ?

[Trucker3573]

I know this has been hashed a bunch and we all know the brand that gets chastised the most for it. I am looking for everyone’s input. Now I can see if the poi starts moving around during your shooting session and the wind hasn’t changed that’s a problem. But from day to day or whatever time frame you pick is it that uncommon ? I watch a particular PB channel on YouTube that puts out a video every single day. He has and does a lot of gun reviews. I’ve seen numerous times where he takes a PB rifle out that was perfectly zeroed at some point prior as I’ve seen it used in prior shooting or hunting vids. In subsequent videos it’s the exact same setup. They almost always require a slight re zero, never being the exact same from previous use

 

[Chukar60]

I believe it is an issue and not just with FX. I have seen people report other makers guns doing the same, just not near as often as FX.
I own several of the most offensive FX guns and it is not an issue for me. My Maverick and neither of my M3’s have suffered the malady unless dropped or some other form of impact has occured and it has to have been significant. It has only happened a few times and both were due to Impacts on the gun.
I had an interesting thing happen this year shooting an indoor league. I thought I was fighting my Maverick 600mm 22. The gun is very accurate but would be shooting 10 rings regularly when I did my part and then would shift low and left. The low and left shots were consistent and overlap the targets presented very good groups. This went on for several weeks until I noticed the gauge for the bottle was reading higher than the tank gauge while filling. Further study showed the bottle gauge was reading 45-50 bar higher than the fill tank gauge. I can usually get 3 full 18 round magazines
+ 6-7 more shots shooting 25.39 pellets. The league is a 30 target course with unlimited sighters. I run the gun with the second reg @ around 135 bar. With the bottle gauge only filling to 195-200 bar I was falling off the reg when I thought I had plenty of air.
Is this the cause of all suspected POI shifts? I doubt it very seriously. However, it is one of many things that can cause a gun to suffer POI shift.
I believe also that the popularity of high magnification FFP scopes with parallax adjustment are another cause because I do not think to many people know how or go through the trouble of making sure their parallax adjustment is as good as it possibly can be. These scopes are particularly fussy at their higher magnifications and at very close range. I will confess that Both the Impact and the Maverick cheek rests are miserable and need an after market riser for them to work for me. Change your cheek weld and you have POI shift.
I agree it happens but I also believe there are more instances where there is a practical and preventable cause.

 

[Ultralight]

Following. This is a problem for me. I'm trying to figure out if it is operator error or some other factors such as temp shift for PCP. I can shoot in cool 70+ degree, and then go to 90 degrees in the noon sun. I wonder if this is a major cause of POI shift for PCP.

 

[Ta-Ta Toothie]

No poi shift with my 600mm King.

 

[kwaping]

It's possible that FX has the most reports of this simply because they are very popular guns.

 

[rcarlisle]

I like to brag about my DreamTac's lack of POI shift. Last weekend, the cattle dog knocked it off the rickety "table". It hit the bench a couple of times on the way down before settling mostly under the table with the butt in the lawn and the barrel against a brace, holding the weight of the gun off the ground. I picked it up and took a shot and found it hitting about 2" left and 1" low at 20 yards. Yikes! I popped the scope off the rail and put it back on in the same position. Took another shot and couldn't tell anything had happened. This weekend's shooting tells me that tumble didn't hurt the gun at all.

 

[Melo]

En mi caso, sufro de cambios de punto de interés. Uso mis armas exclusivamente en un campo de tiro. Este campo está a nivel del mar. Disparo con potencia europea, de 16 a 24 julios, y prácticamente solo disparo con BR a 25 metros.Mis sesiones de tiro casi siempre empiezan temprano, sobre las 8:00 a. m. La temperatura es relativamente fresca, hay mucha humedad y el aire es muy denso. Mis primeros disparos son bajos y compenso con la mira. A medida que sube la temperatura, compenso menos hasta alcanzar el punto óptimo.Bueno, le echo la culpa a las temperaturas. Puede que me equivoque. La verdad es que he aprendido a vivir con ello y no toco la mira telescópica porque sé que se reiniciará sola. Los rifles, un Steyr Challenge, con su chasis de aluminio, es el más espectacular, son muy sensibles a las temperaturas, y en países como Inglaterra hay muchos usuarios que se quejan de ello...

FX Crown .177,es la menos que lo sufre,su culata es de polímero y creo que esto le ayuda bastante,es una carabina maravillosa.

Y por último el FX King .22 con chasis sabell-tactical, todavía estoy luchando con este rifle y estoy empezando a pensar que comprarlo fue un grave error,estoy empezando a comprender que es un rifle diseñado y creado para operar a alta potencia y disparar a largas distancias y yo pretendo lo contrario,el caso es que el rifle funciona perfectamente, y a veces sin tocar nada pasan varios balines por el mismo agujero, pero últimamente noto que los primeros disparos son bajos y lentos (usando el crony) y a los 5 o 6 vuelven a su potencia, siendo el arma muy precisa y consistente.Esto me pasa al principio de una sesión de rodaje, independientemente de la temperatura, o bien después de dejarla un par de horas, y me tiene un poco confundido.Seguiré trabajando en ello por un tiempo, le daré una oportunidad, puede que no sea el rifle perfecto, quizás necesite más experiencia.


125 / 5.0

 

[elh0102]

I believe that anything that fires a projectile through the air is subject to a risk of POI change. Environmental factors will have an influence, but the effects should be relatively minor. That said, I have seen extreme temperature change result in POI shift that was enough to warrant a scope adjustment if in a hunting scenario. As for random, unexplained POI shifts, my rifles with robust barrel mounting designs seem relatively immune from it. These are rifles such as RAW, Taipan Vet I, FX Royale, HW 100, etc. I had an early model FX Crown with liner/sleeve design that was very prone for this behavior, so much that it was unacceptable as a hunting rifle. Since that model, changes have been made in the design, and I assume that the current rifles are more stable. But I've had no further interest in such complex barrel designs, which I see as an unnecessary risk to consistent performance.

 

[EquivalentDelta]

I think a lot of zero problems come from not shooting enough rounds to get a statistically valid average point of impact.


If you shoot a 3 or 5 round group and then adjust, the odds your calculated average point of impact is the true average are very slim. This deception gets worse as the extreme dispersion and the mean radius get larger with less accurate rifles. Imagine putting 5 rounds randomly into 4 moa circle. How many times will those 5 rounds have an average centroid that correlates to the center of the circle? Almost never. So it’s important to fill up that circle.


If your rifle shoots a 0.25moa extreme spread for 20 shots, then you can probably get away with a 3 shot zero. If you’re curious to check point of impact variability try the following formula:


(Accuracy of the rifle in MOA) / (Square root of the number of shots) = (Point of impact variability in MOA)


Minimum number of shots to establish the rifle’s accuracy is 20-30 imo, backed by the guys at Hornady’s ballistic lab.


So my HW77 is a 3.5 moa gun. If I do 5 shots, my potential point of impact variability is : 3.5 / sqrt(5) = 1.565 moa.


Here’s a great demonstration from their podcast. This was real test from a real powderburner. They started with 5 shots. Note the point of impact. Then they kept going to 20 rounds. Look how far the average point of impact “moved” from the 5 round average.

I started shooting 20 rounds to zero my rifle and my “point of impact shifts” disappeared. That’s not to say your rifle doesn’t shift its point of impact. There are mechanical reasons some guns/sights can shift zero.


I can make my HW77 put 5 into a 1moa hole by just tossing cards until I get one. But realistically, it’s a 3-4moa gun if I shoot enough pellets out of the tin.


If I feel like my zero has shifted, I’ll put down 20 rounds and usually find that, no. It hadn’t shifted at all. Either the wind was pushing my rounds off or pure luck put 5 shots on one side of the target.


Just food for thought.

 

[cavedweller]

I think a lot of zero problems come from not shooting enough rounds to get a statistically valid average point of impact.


If you shoot a 3 or 5 round group and then adjust, the odds your calculated average point of impact is the true average are very slim. This deception gets worse as the extreme dispersion and the mean radius get larger with less accurate rifles. Imagine putting 5 rounds randomly into 4 moa circle. How many times will those 5 rounds have an average centroid that correlates to the center of the circle? Almost never. So it’s important to fill up that circle.


If your rifle shoots a 0.25moa extreme spread for 20 shots, then you can probably get away with a 3 shot zero. If you’re curious to check point of impact variability try the following formula:


(Accuracy of the rifle in MOA) / (Square root of the number of shots) = (Point of impact variability in MOA)


Minimum number of shots to establish the rifle’s accuracy is 20-30 imo, backed by the guys at Hornady’s ballistic lab.


So my HW77 is a 3.5 moa gun. If I do 5 shots, my potential point of impact variability is : 3.5 / sqrt(5) = 1.565 moa.


Here’s a great demonstration from their podcast. This was real test from a real powderburner. They started with 5 shots. Note the point of impact. Then they kept going to 20 rounds. Look how far the average point of impact “moved” from the 5 round average.


View attachment 572368


I started shooting 20 rounds to zero my rifle and my “point of impact shifts” disappeared. That’s not to say your rifle doesn’t shift its point of impact. There are mechanical reasons some guns/sights can shift zero.


I can make my HW77 put 5 into a 1moa hole by just tossing cards until I get one. But realistically, it’s a 3-4moa gun if I shoot enough pellets out of the tin.


If I feel like my zero has shifted, I’ll put down 20 rounds and usually find that, no. It hadn’t shifted at all. Either the wind was pushing my rounds off or pure luck put 5 shots on one side of the target.


Just food for thought.

A damaged pellet or a sloppy pellet skirt can greatly reduce FPS thus POI.
Wind... are we really paying attention.. even an indoor ventilation system or fan can blow us off course.
Getting close to or dropping off the reg... yep
Non regulated guns tend to have a sweet zone... too high or too low a fill ..... yep
storing a gun with it leaning against the straw barrel... yep.
leaving the gun / scope in direct sunlight... yep.

 

[Jay308]

Optics can be affected by temps also, some worse than others.

FX issues are it’s own animal. All rifles can shift due to weather conditions etc.

 

[elh0102]

If you shoot 20 rounds to zero a cartridge rifle, the barrel heat will affect POI to the point of influencing an incorrect zero. Depending on barrel profile and stock fitment, the effect can be minor or substantial. But I agree, whether air rifle or firearm, most of us don't shoot enough to yield good results when sighting in.

 

[Jay308]

If you shoot 20 rounds to zero a cartridge rifle, the barrel heat will affect POI to the point of influencing an incorrect zero. Depending on barrel profile and stock fitment, the effect can be minor or substantial. But I agree, whether air rifle or firearm, most of us don't shoot enough to yield good results when sighting in.

For PB’s you better confirm zero the next day.

 

[NamibRose]

It also depends on what scope you have. In example a 1/4 MOA scope might not show a POI change at 100 yards as much as what a 1/10th MOA scope would.

 

[CoyoteGod]

The simple act of sorting weight of pellets and slugs has greatly reduced POI for me. I know many haven’t had much success with sorting but it has made a difference in data for me. I shoot my pellet category weights and my SD and spreads are better and subsequent my POI consistency is better I noticed on all my airguns all the manufacturers I own.

With that said, my most consistent POI shift comes from ambient temperature. I have confirmed this many many times. But I live where shifts in daily temps are often 30 degrees or more from morning to afternoon. Thankfully it has never been so bad that it has caused me problems while hunting morning to afternoon for the most part.

 

[Trucker3573]

If you shoot 20 rounds to zero a cartridge rifle, the barrel heat will affect POI to the point of influencing an incorrect zero. Depending on barrel profile and stock fitment, the effect can be minor or substantial. But I agree, whether air rifle or firearm, most of us don't shoot enough to yield good results when sighting in.

I think most do it with cool downs every so many. Yeah otherwise you will be off on that cold bore shot on an animal.
I just don’t think it’s that unusual to have to slightly adjust your scope after a period of inactivity. See it and experience it all the time. I think that natural tendency gets blamed on the gun.

 

[CoyoteGod]

For PB’s you better confirm zero the next day.

Cold barrel POI shift on PB is not a forgone conclusion. Well made barrels, with excellent throats and chambering, proper stocks/chassis/bedding are much less susceptible to POI. I have very little if any cold barrel issues from my custom PBs, especially with the correct proper hand loads.

 

[JimNM]

It also depends on what scope you have. In example a 1/4 MOA scope might not show a POI change at 100 yards as much as what a 1/10th MOA scope would.

I do believe your are mistaken.

1/4 MAO at 100y = .26 inch
1/10 mil at 100y =.36 inch

Ipso Facto, one click on a standard MOA scope is smaller than 1 click on the standard 1/10 mil scope.

It matters not what a scope will "show" in this question, rather how far the cross hair moves for each click. The "show" would be a matter of zoom power.

 

[Solo1]

I do believe your are mistaken.

1/4 MAO at 100y = .26 inch
1/10 mil at 100y =.36 inch

Ipso Facto, one click on a standard MOA scope is smaller than 1 click on the standard 1/10 mil scope.

It matters not what a scope will "show" in this question, rather how far the cross hair moves for each click. The "show" would be a matter of zoom power.

The problem of poi shift isn’t just related to the barrel. The problem with many fx guns is the number of action parts that are bolted together and move in different temperatures. If you ever shot a poorly bedded action on a pb then had it glass bedded you would understand what im saying.

 

[JimNM]

The problem of poi shift isn’t just related to the barrel. The problem with many fx guns is the number of action parts that are bolted together and move in different temperatures. If you ever shot a poorly bedded action on a pb then had it glass bedded you would understand what im saying.

You claimed a MRAD scope would "show" POI drift more clearly than a MOA scope.

Poppycock says I. All too common for people to confuse POI (ballistics) and POA (optics) - however, that is a topic for another thread.

POI drift in center-fire and rimfire has much more to do with heating and cooling. My PCP collection (no FX in my bunch) does not suffer from POI shift from (gun) internal sources.