Parallax and its effect

A

agw

Guest
To all who care and know?
How do we know if the Parallax of our scope is adjusted corectly and to what extent does it matter. When I only shoot my Bench guns at 50yds will parallax realy matter?

Thanks for your input

Paul
 
Parallax exists when the target and cross hairs are not in the same focal plane in the scope. The way that you tell that you have parallax is to set you rifle up on its rests so that you can view the target through the scope without touching the rifle. If you move your eye, while viewing the target through the scope, and the cross hairs appear to move, relative to the target, you have parallax. I would think it obvious that this condition leads to accuracy problems when trying to shoot precisely since where you are aiming becomes a function of where your eye is behind the scope. Parallax must be determined by inspection. Objective scales are not reliable. Io the other hand, if we are competing in a match, pay no attention to any of the above.:D
 
Boyd

Thanks I will check my adjustments next time out.

I bet you turn "tunners" also

LOL
Paul
 
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Boyd

Another qusetion?
How close of an adjustment matters? What I am thinking is I set up a pratice range,set backer & target stand, Then last summer built two concrete benches. now I need to move my target back 2/3 feet (must remeasure)
So I shoot better at one of the 4 ranges we compete at. I shoot good at my range and at Pala Alto, could the distance be the same??? OR luck
I know there is to many varables to realy answer but someone could have had a simmular experince!
Paul
 
Last edited by a moderator:
agw said:
Another qusetion?
How close of an adjustment matters? What I am thinking is I set up a pratice range,set backer & target stand, Then last summer built two concrete benches. now I need to move my target back 2/3 feet (must remeasure)
So I shoot better at one of the 4 ranges we compete at. I shoot good at my range and at Pala Alto, could the distance be the same??? OR luck
I know there is to many varables to realy answer but someone could have had a simmular experince!
Paul
Click to expand...

Not likely parallax. more likely:
wind ( both magnitude and predictability)
unstable bench
uncomforatable bench
large difference in altitude or temperature.
compeitive pressure or distractions

Theoretically the magnitude of parallax error (bullet impact error at the target) can be as much as:
(target distance - focal distance)/ focal distance) * (objective diameter/2)

For example if you're shooting at a 1000 yard target with a fixed scope focused at 200 yards with a 2" objective the maximum parallax (eye at the edge of the exit pupil) would be (1000-200)/200 * 2/2 = 4 inches of impact error at the target.

If you're shooting a 210 yards and your scope is focused at 200 yards then
(210-200)/200 * 2/2 = .05 inches.

Ther error will be in the same units as you use to measure the objective diameter (inchs or millimeters) The focus range and target range only need to be in the same units. Yards or meters works fine.

It's unlikely you'll position your eye right at the edge of exit pupil since that's noticable, so the maxium parallax error will typically be less that the equation above indicates.

If you suspect that the targets are at different distances at the ranges you shoot at bring a laser rangefinder or a surveyors tape. Most ranges are dead on. A few aren't.
 
Louis, that is...

...the best explanation of parallax I have ever read. Thank you.:)
 
Thanks to BOTH Boyds

I seem to have found two BOYDs that know what the're talkin about.

I will get more comfortable,less distracted,check that twisty thing on front of scope (but not looking at its numbers) and shoot better.
I am trying to understand what makes there rifles tick.
I to like the long version of explantions.
Thanks
Paul
 
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