100m and 200m group size very similiar

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Scrubbit

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Setup as follows:

300 WM/Remington 700 XCR bedded with muzzle brake on 26 in factory barrel/Vortex viper 6-24 FFP/Bipod with sandbags for rear rest/Win brass/210 gr VLDs seated 10 thou of the lands/2830 fps avg at -8 C

I do all my zeroing at 200m, and after being fully zeroed, I figured I'd try shooting at 100m to take wind mostly out of the equation for a more accurate windage zero. The range I shoot at has very uneven side berms, so it's difficult to get a good lateral zero. Avg 5 rd group size at 200m is 1.5in (.75MOA). When I shot at 100m, the avg group size was almost identical. Thought maybe I was doing something differently, so switched back to 200m and group size is still 1.5 in. I checked Litz' book and checked to see if stability was an issue with a 1/10 twist barrel, but it's not even close. Has anyone else experienced this, and if so, do you know what causes it?

Many thanks for any info.
 
Check to see if you have parrelax at 100, but not at 200.

If the scope has a parrelax adjustment, adjust the image so that it is at its clearest/sharpest. Place your rifle into postion on your target (at the range/distance you are shooting).Then, without touching the rifle or bench, move you eye back and forth/up and down in the field of view. If the crosshairs move around the target, there is still parallax present. Adjust the parellax adjustment a little more, untill there is no visible movement.

This parallax adjustment should be done before shooting at any/every distance. As a shooter goes out further, the need for adjustment tends to diminish a little at each successive distance. If I have a scope that has this adjustment, (while hunting) I usually set the adjustment for about the maximum distance I expect to shoot.

"BEAR IN MIND" that the distances that are marked on most parrallax adjustment knobs/objective bells are only guides.
For example: a given scope may be parralax free at 100 yards only when the adjustment is on 50 yards or 200. You will need to figure your individual scope out. It takes some playing around, but you will get it.

Some shooters never/rarely notice this because they either lack the awareness of the image distortion, or they naturally place their eye very close to the center of the field of view in the scope. When your eye is at the exact center of the lense, parallax is normally non exsistant.


If your scope doesnt have this adjustment, just really concentrate on centering your eye in the field of view each and every time. It becomes routine after a while.

I may be mistaken, but, i believe that the higher the magnification, the greater the "potential" for parrallax at each relative distance.

Hope this helps you or anyone else. I am sure some other gunnutz will chime in and help clarify some of my ideas or add more. Thats how we learn.
 
Thanks for the response. I do have a parallax adjustment on the scope, and it's delineated down to 100m, so I can set it to the exact value. I adjusted it to 100m when I was shooting at that range, and back to 200 prior to shooting at that range, so I don't believe that was the cause, although I do have a tendency to forget upon occasion.
 
I am by no means an expert on anything.
But Brain Litz (I think) has a done some work on bullets "going to sleep" which could be part of the issue.

I had the same thing happening with my M14, unfortunately we were talking 2+ inch groups at 100 and 200m, my opinion of my own personal experience was that I was having an easier time "aiming small" on the target at 200m. I could aim more consistently at the smaller target.
 
Normal for 100 and 200, ask a benchrest shooter or look at super shoot scores. 300wm is not easy to shoot.
 
Dumptruck said:
How would paralax affect the group size? I understand how it can shift your point of aim but guess I don't understand fully what is going on.
Click to expand...

If you are shooting with bad parallax, and have your eye in slightly a different position for each shot, it will cause a dispersion in your impact points.

If you have 2" worth of parallax, your smallest potential group is 2" larger than the rifle is actually capable of.
You can basically add the parallax value to your group size that the rifle is capable of.
It just handicaps your ability to shoot more consistantly.

If you take a rifle that is capable of 1/2 MOA accuracy consistantly, and shoot it with a scope that has a very bad parallax adjustment, you will never realise its potential.

I hope I am explaining this adequately, and not confusing the issue! Lol!
 
Scrubbit said:
Thanks for the response. I do have a parallax adjustment on the scope, and it's delineated down to 100m, so I can set it to the exact value. I adjusted it to 100m when I was shooting at that range, and back to 200 prior to shooting at that range, so I don't believe that was the cause, although I do have a tendency to forget upon occasion.
Click to expand...

It seems that you are using the scale on the paralax adjustment knob to set your paralax. I think what dthunter is trying to explain is that the numbers on the adjustment knob are just there as a GUIDE. 100 on the knob may not actually be 100 in actuallity. I have the same scope as you and I set that knob and do the head wiggle every time I change distance i'm shooting at. Get in the scope, adjust the knob for the clearest/sharpest image, wiggle your head around and see if the xhairs are moving on the target, if they are then your paralax is not set. Once you have it set so when you wiggle your head and your xhairs are not moving on the target, then you can shoot paralax free. Ignore that scale on the knob, it means nothing. Set it by your eye, not the scale.
 
Thanks for all the input guys. I wonder if one factor is, as you mentioned, that it's more natural to even out your oscillations when aiming at a more distant target. Kind of like looking far down the road when driving rather than directly in front of the truck. I shoot at a 2 cm diameter bullseye. Parallax error has more of an effect at close range right? Thought I'd read about a bullet settling down in the Litz book, but can't find it now. Need to re-read the book anyway. Gives me an excuse.
 
I have had similar experience and have no explanation that holds water.

Guys often say the bullet needs time to "go to sleep"

The idea is the bullet rotations per unit of forward movement increases as the bullet slows down and this is thought to increase the bullet stability factor. How the bullet magically finds its way toward the center of the group is unexplainable.
 
BadAsMo said:
I have had similar experience and have no explanation that holds water.

Guys often say the bullet needs time to "go to sleep"

The idea is the bullet rotations per unit of forward movement increases as the bullet slows down and this is thought to increase the bullet stability factor. How the bullet magically finds its way toward the center of the group is unexplainable.
Click to expand...

Here is an article about bullets going to sleep.
longrangehunting.c om/articles/bullet-pitch-yaw-1.php
 
Thanks Personal, will check my parallax adjustment next time I'm out and see if the numbers match my eyes
 
Canuck, here's the forum thread associated with the article you mentioned. The 6 degree of freedom simulation is instructive. I guess the way to test it would be to set up aligned targets at successive ranges and fire a group through all of them at once. Sounds like a lot of work to me! Might try some targets at 300 and see if the same holds true, although the model showed most of the oscillations damped out around 200.

http://www.longrangehunting.com/forums/f5/do-bullets-go-sleep-110212/
 
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"Sleepy bullets"? Bullets are just bullets and as long as they exit the crown the same way, they will act the same. If one was trying to convince me that a bullet could go to sleep (especially in 200M), they would need to explain::: A 168SMK exits my 1:12 twist, properly crowned barrel at 2700fps...and without wind or other external factors...it follows the path expected. Another shooter, fires the same bullet out of the same twist barrel at the same muzzle velocity..gets a smaller group at 200M than 100M...and declares the bullet must have not only went to sleep, but it must have self directed towards the group center. I don't think so? IMO, if the sleepy bullet theory was credible, it would occur with every bullet of that exact same design, fired from rifles of the exact same design, at the exact same velocity and rotation...would act the same. If a bullet is off course by 1MOA at 100yds, if unaffected by other factors such as wind, it will be 2MOA off at 200yds.. Epicyclic swirl accounts for a very miniscule change in course and would not be noticible, or possibly even measurable because of human error at the trigger.
 
Hi JEC. Reread the portion of the Litz book on epicyclic swirl, and you're right. Max deflection for a very long relatively unstable 7mm bullet is in the fraction of an inch at the muzzle and basically damped out by 100m. Must be a combination of parallax and aiming error.
 
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