LRaccuracy
Member
- Joined
- Jul 11, 2009
- Messages
- 171
At some point in our shooting experience most everyone learns that one-minute of angle is equal to 1.0471 inches at 100 yards. Most of us ball park this figure to “about an inch” at 100 yards. That always worked for me. I’m happy with that. I’m pretty sure that I will not be able to shoot as well as my firearms are capable of shooting anyway.
I ran some numbers the other day concerning human sighting errors. Actually just some simple calculations in geometry told me why I don’t hit the X every time I pull the trigger.
Here’s what I found. With a sight radius of X inches and with a sighting error of .001” (one thousandths of an inch) of elevation, the bullet will impact by N inches off of your intended target area.
Sight Radius ---------------------- Elevation change ---------- Impact change at 100 yards
13" ---------------------------------.001” ------------------------ .2769”
14" ---------------------------------.001” ------------------------ .2571”
15" ---------------------------------.001” ------------------------ .2400”
16" ---------------------------------.001” ------------------------ .2250”
17" ---------------------------------.001” ------------------------ .2118”
18" ---------------------------------.001” ------------------------ .2000”
This may not surprise you but it surprised me. That means if I have a rifle with a sight radius of 18 inches and I am shooting at a target 100 yards away AND my sight picture is off by two thousandths of an inch, I miss my target by .4 inches. The sighting error is not even the width of a human hair.
Okay now everyone can tell me that they knew this. I must have been living with my head in the sand.
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The below was added after posting the original thread:
I did the calculation on a 4" sight radius at 25 yards and this will floor you.
With only .01" (one-hundredth of an inch) sighting error at 75 feet, the impact of the bullet will change by a whopping 2.25".
Sight Radius ----------------- Elevation change ---------- Impact change at 25 yards
4" --------------------------------- .01” ------------------------ 2.25”
I ran some numbers the other day concerning human sighting errors. Actually just some simple calculations in geometry told me why I don’t hit the X every time I pull the trigger.
Here’s what I found. With a sight radius of X inches and with a sighting error of .001” (one thousandths of an inch) of elevation, the bullet will impact by N inches off of your intended target area.
Sight Radius ---------------------- Elevation change ---------- Impact change at 100 yards
13" ---------------------------------.001” ------------------------ .2769”
14" ---------------------------------.001” ------------------------ .2571”
15" ---------------------------------.001” ------------------------ .2400”
16" ---------------------------------.001” ------------------------ .2250”
17" ---------------------------------.001” ------------------------ .2118”
18" ---------------------------------.001” ------------------------ .2000”
This may not surprise you but it surprised me. That means if I have a rifle with a sight radius of 18 inches and I am shooting at a target 100 yards away AND my sight picture is off by two thousandths of an inch, I miss my target by .4 inches. The sighting error is not even the width of a human hair.
Okay now everyone can tell me that they knew this. I must have been living with my head in the sand.
------------------------------------------------------------------------------------------------
The below was added after posting the original thread:
I did the calculation on a 4" sight radius at 25 yards and this will floor you.
With only .01" (one-hundredth of an inch) sighting error at 75 feet, the impact of the bullet will change by a whopping 2.25".
Sight Radius ----------------- Elevation change ---------- Impact change at 25 yards
4" --------------------------------- .01” ------------------------ 2.25”
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