Accuracy is not linear
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Old 04-09-2010, 05:40 PM   #1
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Default Accuracy is not linear

Example, if a rifle shoots 1 MOA @ 100 yards, it does not mean it will shoot 10 MOA @1000 yards.

I know this(or think i know it). But I can't explain fully why. The biggest variable I am assuming is wind, but what other variables come into play? Exclude the shooter from this discussion, i guess that actually is the biggest variable.

Wind
bullet
powder amount
powder burn consistency
scope
velocity

What am I missing from the list?


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Old 04-09-2010, 05:50 PM   #2
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Quote:
Originally Posted by Yunus View Post
Wind
bullet
powder amount
powder burn consistency
scope
velocity
How about "distance" as well, but that was kind of implicitly included in your post.


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Old 04-09-2010, 05:52 PM   #3
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Also, here's some information on how to calculate Minute of Angle:

What is Minute of Angle
Mil-dots and Minutes-of-angle - From a Technical Perspective
Minute of Angle - Wikipedia, the free encyclopedia
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Old 04-09-2010, 05:55 PM   #4
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Although not as large a factor as wind deflection, gyroscopic drift, or spin drift as its commonly referred to as is an issue for long range shooting, and something worth considering.
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Old 04-09-2010, 06:01 PM   #5
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  • Wind on multiple axis ( Head, tail, cross, angled )
  • Effects gravity will play on the round
  • Reduced velocity as it goes further, compounding gravity's effect
    • Super sonic vs. sub sonic speed of the round
    • By-product is FPS as round leaves barrel
    • Overspin / balance of the rounds center - leading to:
  • Spin Drift
  • Mirage
  • Humidity from zero location to location of shot taken from
  • Elevation from zero location to location of shot taken from
You also have to factor in Ballistic Coefficient of the round and realize that some rounds will REACH 1000 yards, but will not be truly spinning on their true centralized axis.

This condition is why some shooters in benchrest mic and test their reload bullets in a sectional density solution to check for consistency.

You have realize that when you are shooting 1,000 Yards, it will truly be one of the hardest things you will ever do. It really is THAT hard even with good equipment....
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Old 04-09-2010, 06:20 PM   #6
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1moa at 100 yards is aprox 1" 1 moa at 500 yards is 5" 1 moa at 1000 yards is 10" or there abouts.

If a rifle shoots 1moa at 100 yards that does not mean it will shoot 1moa at 500 yards.

There are umpteen hundreds of things that affect bullets accuracy.
1. Distance
2. spin
3. wind
4. friction coefficient of barrel
5. friction coefficient of bullet
6. air density
7. humidity
8. elevation
9. gravity
10. Rotation of the earth
11. consistency of barrel (Variations in diameter).
12. consistency of powder burn rate
13. consistency of primer burn
14. consistency of brass
15. consistency of seating depth of bullet
16. consistency of neck tension on bullet
17. consistency of bullet diameter
18. consistency of bullet jacket thickness
19. barrel lock up
20. lug engagement.
and others that I am not thinking about.

There is a lot of factors that go into accuracy of a rifle. Also a rifle that shoots 2moa at 100 yards will never ever shoot below that at longer distance. I don't care what anyone says it just can't happen.
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Old 04-09-2010, 06:52 PM   #7
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I'm no where near being able to shoot at 1000 yards, I would like to try to work up to 500 someday but not anytime soon, biggest reason, is lack of a range that goes that far.

Thanks for the responses they were what I was looking for. This is more of a mental exercise than a real world thing for us. I was just trying to figure out what goes into the shot, assuming the shooter is out of the equation, and you guys delivered .
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Old 04-09-2010, 09:06 PM   #8
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Quote:
Originally Posted by Yunus View Post
Wind
bullet
powder amount
powder burn consistency
scope
velocity

What am I missing from the list?
Gravity
Elevation - air density, etc

As Tango states the list is long...
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Old 04-10-2010, 03:18 AM   #9
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That "Rotation of the Earth" part is interesting. It does come into play at 1000 yds. I'm suprised that a bullet traveling that fast would be affected by this, but it is.
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Old 04-10-2010, 06:56 AM   #10
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Quote:
Originally Posted by kansas45 View Post
That "Rotation of the Earth" part is interesting. It does come into play at 1000 yds. I'm suprised that a bullet traveling that fast would be affected by this, but it is.
It's called The Coriolis Effect

The Coriolis Effect occurs as a consequence of the fact that you're shooting from one point to another on a rotating planet (the Earth) The Coriolis Effect is very minor, and can be disregarded for most practical shooting applications.

Heres some basic facts about the Coriolis Effect

1. The Coriolis Effect has both vertical and horizontal componets which are independent.
2. The horizontal component of the Coriolis Effect is entirely determined by your latitude on Earth, and is unaffected by the azimuth of fire.
3. For latitudes north of the equator, the horizontal component of the Coriolis Effect is always to the right. For latitudes south of the equator, the deflection is to the left.
4. The horizontal Coriolos deflection is minimal at the equator, and grows greater as you move toward the poles.
5. The vertical component of Coriolis deflection depends on your latitude and azimuth of fire.
6. Fireing east will cause you to hit high, and fireing west will cause you to hit low.
7. When shooting north or south, the vertical component of /coriolis deflection is zero regardless of latitude.

Reference: Applied Ballistics For Long Range Shooting
By Bryan Litz


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