Movement at 100 Yards

D

Dew

Guest
This is a quote from another post. "A .001" movement at the rifle equates to approximately 1/4" movement on the target at 100 yards". Years ago I asked the same question and was told by someone whom I think would know that the answer was one inch. I am talking about the barrel movement at the muzzle in a right to left hand direction. Or vice versa. Is this not correct?


Dew
 
Dew ...

Dew said:
This is a quote from another post. "A .001" movement at the rifle equates to approximately 1/4" movement on the target at 100 yards". Years ago I asked the same question and was told by someone whom I think would know that the answer was one inch. I am talking about the barrel movement at the muzzle in a right to left hand direction. Or vice versa. Is this not correct? Dew
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That was from part of my post. I should have provided the source. Here it is: The Benchrest Shooting Primer [from Precision Shooting Magazine], Page 228, Right Column article, The Weak Link, by Lt. Col. Rick Hornbeck, first paragraph.:)
 
Actually, I believe that a .01" movement will move the point of impact 1 inch at 100 yards. .001" would move the point of impact approx 1/8 ".
 
Depends on rifle length. A 36" rifle will have a larger arc from butt to crown with 0.01" total muzzle movement then a 46" rifle with the same muzzle movement.
 
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abintx

Thanks for that post. I MAY have forgotten what I thought I read some years ago. I'm sure that reference would be correct.

Dew
 
Once more into the breach

Now as to the posts above....

How do you show that the distances involved are done with math?
You DO understand that I have trouble with my telephone bills. I don't know how they come up with the things they do. They being the phone company of course. :)
 
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Dew said:
Now as to the posts above....

How do you show that the distances involved are done with math?
You DO understand that I have trouble with my telephone bills. I don't know how they come up with the things they do. They being the phone company of course. :)
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Here's a trig-free way to think about it. Just use proportions.

If your rifle is 4 feet long, and you move the muzzle 0.001 inch while keeping the toe of the stock fixed in place, you have a "taper" of 0.001"/4ft. At 100yd (300ft) the displacement will be (300ft/4ft)*0.001"=0.075" -- a little over 1/16".

If a *scope* is off by 0.001", the bullet displacement at 100yd will be much greater, because the scope is roughly 3 times shorter than the rifle. A 16" scope (1.3ft) moved 0.001" would move the point of aim (300ft/1.3ft)*0.001"=0.231" (about 1/4").

Toby Bradshaw
baywingdb@comcast.net
 
Sumthin' don't sound right...

I grasp the simple math statements and accept the logic of them. But I keep thinking about the real life situation of shooting groups.
Accepting that .001 scope movement causes about a 1/4" of impact movement on the target, imagine what .005 or .010 does, 1 1/4" to 2 1/2" bullet movement on the target.
A hunting rifle with a normal crosshair, say at 7X or 9X would be very difficult to align within a few thousandths of an inch. Five shot groups would probably be 3"-5" minimum. And that does not happen very often. I've shot hundreds of groups with friends hunting rifles at my home range and know that most rifles are more accurate than their owners.

What am I not understanding?

Jay, Idaho
 
Don't worry about it. I'm still working on this last phone bill:)

Dew
 
Now the erector tube in a commonly used BR scope is maybe
2 1/2 inches long from its forward support point to where the adjustments
are located. That 100yds equal 3600 inches. 3600 divided by 2.5 inches
gives a ratio of 1440 to 1. Should your erector tube fail to return by .001
the error on target would be 1.44 inches. 5 tenths still puts you in last place.
 
Jay said:
I grasp the simple math statements and accept the logic of them. But I keep thinking about the real life situation of shooting groups.
Accepting that .001 scope movement causes about a 1/4" of impact movement on the target, imagine what .005 or .010 does, 1 1/4" to 2 1/2" bullet movement on the target.
A hunting rifle with a normal crosshair, say at 7X or 9X would be very difficult to align within a few thousandths of an inch. Five shot groups would probably be 3"-5" minimum. And that does not happen very often. I've shot hundreds of groups with friends hunting rifles at my home range and know that most rifles are more accurate than their owners.

What am I not understanding?

Jay, Idaho
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;)


It's a visualization thing Jay. The movement we're talking about is the sort which promotes a twisting about the gun's vertical axis. If muzzle moves .001 to the right or left while pivoting on the axis of the scope reticle or in other words you're holding fine but the muzzle is misaligned clear back at the point of origination (the firing line) ........ then the misalignment is magnified by the distance.

The movement you're visualizing is converging on the target and furthermore "holding a thou or twenty off" on target is just that, a thou or twenty........ no magnification nor extrapolation.

then again, maybe I'm completely missing your question

al
 
If it was me, I'd shoot a couple of sighters. ;):rolleyes::cool: But, I've learned that you can't trust sighters either. Or flags.:eek:

Maybe that's why I'm off paper at 1000 yards. .001" x 1000 yards x the square of the hypotinuse. Yikes!


ray
 
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A real-world usage.....

Harold Vaughn (gotta' LOVE the guy!) actually applied something more than guesswork to the thing. He took some guns, and took up a hammer and punch....... and gently tapped the scope bases this way and that.

The results were nothing short of startling. To me anyways. I've aligned and bedded and glued down my scopes ever since.

Kokopelli and Epoxy make for a good combination. :)

al
 
FBecigneul said:
I'll wish you all Happy April Fools day.
It must be February or March judging by the topic.
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I don't feel this way at all. I think a bunch of 'defective scopes' can be traced to improper mounting support.

Using a Hood's Scope Checker will often move the scope bases. Doesn't change the effectiveness of the checker, just makes you hit funny.

al
 
I've been having issues maintaining a zero with one of my rifles, sent the scope on it back for repair & bought a new one meantime - only to find that the issue didn't go away. Finally, I pulled the mounts off the scope preparatory to installing another brand I had & damned if the base of both the original mounts didn't fall apart at the point where the clamping cut came close to the ring.

I won't mention the breed as I had replaced the slotted lock screws with cupheads & probably leaned on them a tad assertively, but in any case, even knowing that I was probably at fault, the supplier replaced the rings at no cost to me.
 
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