i have a Gamo Whisper IGT .22, amazing rifle and puts pellets ontop of pellets.. now my scope is zeroed in at 40yrd, but at, say 20 yard the pellets are hitting low, whereas they should be hitting high?
The scope is mounted above the bore on the rifle. Because of that, the pellet starts out roughly 1" to 2" LOW- whatever the distance between the bore and the center of your scope's optics. For the pellet to hit where the crosshairs are aiming at 40 yards, it must actually move UPWARD. That's because, when you're holding your rifle to aim it at a target 40 yards away, you're holding it so that the barrel points slightly upward- hence the pellet's height increases.
Now, if you aim at something 20 yards away with your scope zeroed at 40 yards, the pellet has only traveled half as far, and has therefore increased its height roughly half as much (yes, I know it's not EXACTLY half, but I'm using that for the sake of simplicity).
So your rifle is doing exactly what it's supposed to do, and so is the scope. The pellet will continue rising until it hits roughly 40 yards, and may actually increase in height past that depending on the ballistics of your chosen load.
Projectiles move in a parabolic arc, rising then falling. Your scope should be zeroed at 2 distances, one on the rise, the other on the fall. You are likely zeroed on the rise for 40 yards, so at 20 yards the pellet is still rising. No matter how level you feel like you are holding a firearm, you aren't, when aiming at something you are pointing slightly upwards.
Why "should" they be hitting high? The projectile moves in an arc, the line of sight of the optic is a straight line that starts out a couple inches above the starting point of the projectile arc. That arc of the projectile crosses or touches the the line of the sight at the point where it's zeroed. For most trajectories/zeroes, the projectile would still be on the upward part of the arc halfway between the muzzle and the distance zeroed, and therefore would be a tad low yet.
There is only one answer that makes sense to me--the pellets are still on the rise at 20 yards. Consider the height difference between where you sight and your muzzle opening. Do you have a scope that increases this difference? If so, then it is more understandable. Try shooting the intermediate ranges for the answer: 10 yds, 30 yds.
To the best of my knowledge, the American version of the Gamo Whisper IGT and it's variants all deliver "around" 15ft-lbs of muzzle energy. Which means they deliver around 700fps with average weight(14gr) pellets
Gamo does have a 20ft-lb powerplant(Varmint Hunter HP and variants), but, like I said, none of the "Whisper" rifles, that I'm aware of use the 20ft-lb powerplant.
Gamo claims "up to a maximum of 975fps" for some of their air rifles which include Whisper in their name. >In actual testing(chronograph) I have not seen muzzle velocities, even with ultra lightweight alloy pellets. Which achieve that claim<
What's going on here?
The only way I can calculate that(low at 20 yards with a 40 yard zero) as a possibility is if your rifle is pushing ultra lightweight alloy(low BC) pellets at around 1000fps and you're using a high set of rings.
With a .22 caliber air rifle I attempt to keep the hold over/under to around one inch or less. For as much of the effective range of the rifle as possible.
Example
690fps with 14.3gr CPD / 40 yard zero
10 yards = + .1 inch
20 yards = + .86 inch
25 yards = +1.01 inch
30 yards = + .92 inch
45 yards = - 0.86 inch
50 yards = - 2.01 inch
In this example, 40 yards would be a good sight-in range.
I am not a rifle shooter...BUT.....you scope is on top of your rifle right? If so....then the closer you get to the target the lower the pellet should hit. Coming out of the muzzle the pellet is below the scope- right?
picture your scope crosshairs and the muzzle of the barrel forming a triangle to a target you have set your scope to zero at ...the triangle intersects at your zero point and then opens up the opposite direction as you move further out from the zero-point target .. if you trace the line that represents your muzzle back from the zero-point target you can see it will be lower as you head towards the gun, and higher as you go out past the target .. but of course distance will add drop into the equation ..
Comments
You're confused.
The scope is mounted above the bore on the rifle. Because of that, the pellet starts out roughly 1" to 2" LOW- whatever the distance between the bore and the center of your scope's optics. For the pellet to hit where the crosshairs are aiming at 40 yards, it must actually move UPWARD. That's because, when you're holding your rifle to aim it at a target 40 yards away, you're holding it so that the barrel points slightly upward- hence the pellet's height increases.
Now, if you aim at something 20 yards away with your scope zeroed at 40 yards, the pellet has only traveled half as far, and has therefore increased its height roughly half as much (yes, I know it's not EXACTLY half, but I'm using that for the sake of simplicity).
So your rifle is doing exactly what it's supposed to do, and so is the scope. The pellet will continue rising until it hits roughly 40 yards, and may actually increase in height past that depending on the ballistics of your chosen load.
No, your scope is not messed up.
Projectiles move in a parabolic arc, rising then falling. Your scope should be zeroed at 2 distances, one on the rise, the other on the fall. You are likely zeroed on the rise for 40 yards, so at 20 yards the pellet is still rising. No matter how level you feel like you are holding a firearm, you aren't, when aiming at something you are pointing slightly upwards.
Why "should" they be hitting high? The projectile moves in an arc, the line of sight of the optic is a straight line that starts out a couple inches above the starting point of the projectile arc. That arc of the projectile crosses or touches the the line of the sight at the point where it's zeroed. For most trajectories/zeroes, the projectile would still be on the upward part of the arc halfway between the muzzle and the distance zeroed, and therefore would be a tad low yet.
There is only one answer that makes sense to me--the pellets are still on the rise at 20 yards. Consider the height difference between where you sight and your muzzle opening. Do you have a scope that increases this difference? If so, then it is more understandable. Try shooting the intermediate ranges for the answer: 10 yds, 30 yds.
Edit
I have added this top part.
To the best of my knowledge, the American version of the Gamo Whisper IGT and it's variants all deliver "around" 15ft-lbs of muzzle energy. Which means they deliver around 700fps with average weight(14gr) pellets
Gamo does have a 20ft-lb powerplant(Varmint Hunter HP and variants), but, like I said, none of the "Whisper" rifles, that I'm aware of use the 20ft-lb powerplant.
Gamo claims "up to a maximum of 975fps" for some of their air rifles which include Whisper in their name. >In actual testing(chronograph) I have not seen muzzle velocities, even with ultra lightweight alloy pellets. Which achieve that claim<
What's going on here?
The only way I can calculate that(low at 20 yards with a 40 yard zero) as a possibility is if your rifle is pushing ultra lightweight alloy(low BC) pellets at around 1000fps and you're using a high set of rings.
Airgun Forum
http://www/network54.com/forum/79537
If you ask here, someone might be able to come up with an explanation.
Because I sure can't think of one that both makes sense and falls within the capabilities of your rifle.
____________
Realistically
If you have chronograph numbers for your rifle/pellet combo
Use the calculator below.
Pellets / BC(Ballistic Coefficient)
Crosman Premier Domed(14.3gr) - 0.025
RWS Superdome(14.5gr) - 0.016
JSB Exact Domed(15.89gr) - 0.031
H&N Field Target Trophy(14.66gr) - 0.029
If you're using another pellet, an estimate should give you reasonably close results.
If you don't have chronograph numbers. I would estimate the MV at around
690fps with the 14.3gr CPD
685fps with the 14.5gr RWS SD
680fps with the 14.66gr H&N FTT
655fps with the 15.89gr JSB
Airgun Trajectory Calculator
http://www.airguns.net/trajectory.php
Optimum zero range
With a .22 caliber air rifle I attempt to keep the hold over/under to around one inch or less. For as much of the effective range of the rifle as possible.
Example
690fps with 14.3gr CPD / 40 yard zero
10 yards = + .1 inch
20 yards = + .86 inch
25 yards = +1.01 inch
30 yards = + .92 inch
45 yards = - 0.86 inch
50 yards = - 2.01 inch
In this example, 40 yards would be a good sight-in range.
No...
I am not a rifle shooter...BUT.....you scope is on top of your rifle right? If so....then the closer you get to the target the lower the pellet should hit. Coming out of the muzzle the pellet is below the scope- right?
picture your scope crosshairs and the muzzle of the barrel forming a triangle to a target you have set your scope to zero at ...the triangle intersects at your zero point and then opens up the opposite direction as you move further out from the zero-point target .. if you trace the line that represents your muzzle back from the zero-point target you can see it will be lower as you head towards the gun, and higher as you go out past the target .. but of course distance will add drop into the equation ..