sighithing in slug shot gun
- Thread starter a_styer_95
- Start date
Brutus
CGN Ultra frequent flyer
I notice that many relatively short barrelled smoothbore shotguns shoot slugs high for point of aim.
One way manufacturers addressed this is by putting the factory bead on a ramp or pedestal.
This Ithaca was modified by the previous owner for that very reason:
And this 870 came this way from the factory for the same:
One way manufacturers addressed this is by putting the factory bead on a ramp or pedestal.
This Ithaca was modified by the previous owner for that very reason:
And this 870 came this way from the factory for the same:
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I got this formula off CGN at some point, I cannot recall when or who posted it.
You need to measure your actual distance between front edge of rear sight and rear edge of front sight blade and use it in the calculation instead of the example value of 18.55” to determine how far your front site needs to be raised.
POImpact – POAim
S x D ÷ (R x 12) = M
Where:
M = amount of change in sight height needed (in INCHES).
S = distance between front edge of rear sight and rear edge of front sight blade (sight radius in INCHES).
D = distance in inches needed to move the bullet's strike to hit point of aim.
R = range to target (in FEET).
Example:
Slugs hit 6 inches high at 25 yards.
Your sight radius is 18.55 inches and you need to move the bullet's strike 6 inches lower at 25 yards (75 feet):
(18.55” x 6”) ÷ (75 x 12) = M
111.3 ÷ 900 = .124”
The front sight needs to be raised (or lower rear sight) by .124 inches.
Your math is, of course, correct.
calculator here, range is in inches:
"http://www.brownells.com/.aspx/lid=13093/GunTechdetail/Sight_Correction_Calculator
Getting hit by a slug that is impacting 6" high will still hurt.
Using a two bead system on a vent rib, my 26" open cyclinder groups 3" at 50 yards and is 3" low and right.
Since slugs are like pumpkin balls where is it impacting at 50 yards.
Have you changed brands of ammo to try to change point of impact?
Are you using 3" mag versus 2 3/4".
So many variables.
Another rule of thumb for moving a front sight is to "chase your POI". Since you want to raise your front sight you also would want to lower your rear sight.
Using a two bead system on a vent rib, my 26" open cyclinder groups 3" at 50 yards and is 3" low and right.
Since slugs are like pumpkin balls where is it impacting at 50 yards.
Have you changed brands of ammo to try to change point of impact?
Are you using 3" mag versus 2 3/4".
So many variables.
Another rule of thumb for moving a front sight is to "chase your POI". Since you want to raise your front sight you also would want to lower your rear sight.
A red or green dot will correct all errors, if you dont have bases, the barrel cross is great and very sturdy, it will get surprising accuracy from a rifled slug (smooth bore ) or in the case of the NEF Survivor 410-45 Colt with a barrel twist, take a look... JP.
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nowarningshot
CGN Ultra frequent flyer
Norton: forum rule.....there will be no math.
But seriously.....gotta go back again....there will be no math. I should think that any gunsmith will have a orphan sight, that can be attached for far cheaper than the headache ....of working on the math.
Geezee
But seriously.....gotta go back again....there will be no math. I should think that any gunsmith will have a orphan sight, that can be attached for far cheaper than the headache ....of working on the math.
Geezee
Keep all your measurements in inches. Very simple not rocket science.
25 yds is 900 inches
sight radius 18.55 inches
Sight radius 18.55 divide by 900" is .0206" that is how much sight movement to change the poi 1"
multiply that by the amount of change you need and you are done. .0206" x 6" is .1236" looks like 1/8" will suffice.(.0125")
Use 900 for 25 .yds
1800 for 50 .yds
3600 for 100 .yds
My 2¢
R
25 yds is 900 inches
sight radius 18.55 inches
Sight radius 18.55 divide by 900" is .0206" that is how much sight movement to change the poi 1"
multiply that by the amount of change you need and you are done. .0206" x 6" is .1236" looks like 1/8" will suffice.(.0125")
Use 900 for 25 .yds
1800 for 50 .yds
3600 for 100 .yds
My 2¢
R
fat tony
CGN Ultra frequent flyer
I had a similar problem. I just ended up calculating the front sight height correction this way.
I first measured the front sight height above the muzzle outside diameter and recorded it on a notepad.
After shooting at twenty five yards I noted the height the group center was from the center of the bull and recorded it in my notepad.
I measured the distance from the rear sight to the front sight, recording it.
I drew two similar right triangles.
The first represented the sight radius (adjacent side,) and the side opposite (x.) The x represents the unknown sight correction in decimal inches, or if you prefer, decimal feet. Currently unknown either way.
So you got your known sight radius in decimal feet or decimal inches, maybe arshins if you are a retro geek.
Drew another triangle. This one had the distance from muzzle to target (units of your choice) this is the adjacent side of the right triangle. The side opposite is the distance measurement from the center of your group to the centre of the bull. On the big triangle you have two knowns.
All you do now is make up a simple equation.
(Sight radius) is to (x)
And
(Distance to target) is to (vertical distance from group centre to centre of bull)
Isolate the unknown variable.
( distance to target x vertical distance from the bull)÷(sight radius) =x
This works for shooting under or over. The x value in your case is how much taller your front sight needs to be. I had to subtract as my front sight was too high.
What I described is exactly what everyone else said. No trigonimetry required although you could do it that way using the law of sines and other black magic, if you wanted to check your work.
Oops necro thread sorry. Maybe someone else is having the same problem.
I first measured the front sight height above the muzzle outside diameter and recorded it on a notepad.
After shooting at twenty five yards I noted the height the group center was from the center of the bull and recorded it in my notepad.
I measured the distance from the rear sight to the front sight, recording it.
I drew two similar right triangles.
The first represented the sight radius (adjacent side,) and the side opposite (x.) The x represents the unknown sight correction in decimal inches, or if you prefer, decimal feet. Currently unknown either way.
So you got your known sight radius in decimal feet or decimal inches, maybe arshins if you are a retro geek.
Drew another triangle. This one had the distance from muzzle to target (units of your choice) this is the adjacent side of the right triangle. The side opposite is the distance measurement from the center of your group to the centre of the bull. On the big triangle you have two knowns.
All you do now is make up a simple equation.
(Sight radius) is to (x)
And
(Distance to target) is to (vertical distance from group centre to centre of bull)
Isolate the unknown variable.
( distance to target x vertical distance from the bull)÷(sight radius) =x
This works for shooting under or over. The x value in your case is how much taller your front sight needs to be. I had to subtract as my front sight was too high.
What I described is exactly what everyone else said. No trigonimetry required although you could do it that way using the law of sines and other black magic, if you wanted to check your work.
Oops necro thread sorry. Maybe someone else is having the same problem.
Jonnyofalltrades
Regular
- Location
- North-central Saskatchewan
Would be interesting to know how much more hold-off would be required at, say 50 yards?
fat tony
CGN Ultra frequent flyer
He was probably using say Federal Power Shock 1 oz slugs. Remington and Winchester are in the ball park. With the rounds hitting 6" high at twenty five yards, they will be rising another four inches before they come back down again. A slug is not for long range, likely he was going to be woods hunting. It does not seem instinctive to have to stop and take more time to adjust. It is a pita to calculate imagined sight corrections with iron sights on a range where things are slow and controlled but whatever. Also it sounds a bit dangerous to have that much hold under while woods hunting?
Nine year old thread lol. How is our dear op anyways?
Nine year old thread lol. How is our dear op anyways?
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The rounds do not rise at all, they drop after leaving the barrel and continue to drop and never rise... sights have to be adjusted so they intersect the trajectory of the projectile at some point.
Ahhhhhhhh!
Who revives old threads? How deep to you go to find them?
fat tony
CGN Ultra frequent flyer
I made a mistake but a_styer_95 posts stuff that is worth replying to.
He said his gun was putting the holes 6" high at 25 yards.
The gun is angled up way too much. Still the rounds are going to rise approximately 2" - maybe 3" more before they come back down. It is like shooting on a slope, that is why I said approximately.
He said his gun was putting the holes 6" high at 25 yards.
The gun is angled up way too much. Still the rounds are going to rise approximately 2" - maybe 3" more before they come back down. It is like shooting on a slope, that is why I said approximately.
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