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Can rear sight height be higher than front sight?

Posted: Tue Feb 22, 2011 10:22 pm
by 10mair
Like the attached picture, I am thinking of adjust my rear sight higher than the front sight. I wonder if this causes any defect or problems in
shooting 10m air rifle.

Also, I want to know why both rear and front sight must be at the same height. Is there any 10m air rifle player who has set those two at different height?

Thanks in advance.

Posted: Wed Feb 23, 2011 12:21 am
by Pat McCoy
Using a standard sight picture, raising your rear sight will cause the shots to impact higher on the target.

What are you trying to accomplish/

Posted: Wed Feb 23, 2011 3:06 am
by RobStubbs
If the sights are not parallel to the barrell then the shots won't go where you're aiming. In your picture you'd be shooting the backstop above the target.

Rob.

Posted: Wed Feb 23, 2011 6:44 am
by tsokasn
A direct answer to your question is Yes.
As a matter of fact ,as the distance of both front and rear sights increases from the barrel axis(sight risers)the greater the difference between the two will be(sorry for my English)
You may insert the same height sight risers,but the peep sight of the rear iris will go higher in order to bring the projectile to the aiming point.
The result will be a rear iris clicked higher form the center of the rear sight,which of course is not a problem for ten and fifty meter shooting,but is a problem at high power rifle.
In my case,for my air rifle and my standing position,I use the max of permitted sight risers plus for mm extra at the rear sight(to get the iris at the center of the rear sight,but hey, it's just me and it works without the extra 4mm)

I hope you understood me!

Posted: Wed Feb 23, 2011 10:56 am
by KennyB
Think of it like this:

Image

If you want to raise the rearsight, you must also raise the foresight proportionately.
When you alter your sights - what you are REALLY doing is altering the angle of the rifle - the sightline (eye > rearsight > foresight > target) should always be the same for a perfect aim.
So by making the rifle point higher or lower, you get a point of impact at the target that is higher or lower.

Posted: Wed Feb 23, 2011 11:46 am
by Soupy44
Say you put a 4mm riser on the rear sight to accomplish what you propose but leave the front sight as it is. You will end up clicking your rear sight down such that your rear iris drops the 4mm you just added. The height of the sight line is determined by the front sight height, not the rear sight.

thanks for your replies

Posted: Thu Feb 24, 2011 1:25 am
by 10mair
all helped a lot. thanks!

Posted: Thu Mar 03, 2011 3:48 pm
by FrankD
For 10m air rifle you can use max. 60 mm (ISSF Rule) for your front sight, measured from the middle of the barrel to the middle of the front sight. Then you have 60 mm + x on the rear sight, because the rear sight is always a little bit higher then the front sight, as explained in the last postings. To hit a target on certain distance you need always a definite relationship between the front and rear sight.

The projectile on earth goes always a ballistic path to the ground. So, if you have the sights parallel to the barrel, the projectile wont never hit your aiming point.

In the picture from KennyB you can see the sightline hit the ballistic path at two points. For airguns often the rear sight is adjusted to the first point from the barrel and for other guns to the second point. So if you go nearer to the target with your airgun, the hits will drop.

For 50 m smallbore (ISSF) there is no limit for the sights.


Best wishes from Germany and excuse my bad English

Frank

Posted: Tue Mar 08, 2011 8:59 am
by robf
as above, your rearsight will always be a bit higher in the centre than the foresight.

for 10m the effect of gravity is minimal, what the sights are mostly doing is trying to defeat the distance from the foresight centre to the bore centre.

Posted: Tue Mar 08, 2011 10:23 am
by justadude
Assuming constant velocity of 175 meters per second from the muzzle to the target (no deceleration due to air drag) I get a flight time of 0.057 seconds and a drop due to gravity of about 16mm. My bore centerline to front sight centerline is about 40mm so in reality the relations and angles must be set up to overcome the 40mm centerline difference plus an additional 16mm gravity drop.

Assume 10m from front sight to target and 0.8m sight radius and I get a rough estimate the rear sight will need to be about 4.5mm above the front sight. Due to the assumption of constant velocity the drop due to gravity is underestimated so it will need to be a bit more but this is a decent first order estimate.

Bottom line, you cannot arbitrarily move the rear sight without also moving the front sight. The front and rear sight must be in a pretty specfic relationship to one another if you expect to shoot tens.

'Dude