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High magnification scope error?

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/05/2013 at 19:39
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How do you conclusively prove the high magnification of high end scopes is not causing grouping errors?

For example my friend's 8-25x Leupold shoots better groups at 8x than at 25x, and the same appears to be true of my 8-80x March. Both these rifles are capable of one hole groups at 100yds and it seems strange that the better groups are at the lower power.

I know the bench-rests guys dismantle their scopes and glue all the internals securely to prevent any chance of error, and variable power scopes need fractional clearances to allow the lens to move and maybe they are. 

We shoot 100- 1000yds with strong mirage most times so we cannot use a "fixed power or glued" scope.

Your views would be appreciated

 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/05/2013 at 19:53
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I have noticed, that I try way way to hard when my scope is turned up, at close range! I really shoot better at the 10-15x range when at 100. As a matter of fact, I usually don't remember to turn mine up past that point unless I am spotting for someone else.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/05/2013 at 20:01
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Thanks mate, we can set up on bench-rest stand at front and rear bag so any power is easy to hold. We are thinking that maybe there is some internal clearance (that is required by vari-power scopes) that is magnified as the power increases
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/05/2013 at 20:35
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I'm going to call "SHOOTER ERROR".  A few years ago, Richard Wild set a record using the March 8-80.  An Australian record, I believe, but a record none the less and nothing to laugh at or criticize.  I seriously doubt his ability to do that if there were a scope design flaw.
 
At 80x, sight picture/cheek weld is CRITICAL.  Consistent, exact placement is mandatory.  Your exit pupil at that power in that scope is 0.7.  Highly subject to parallax error.  What you need is a 160mm objective...
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/05/2013 at 20:51
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Originally posted by Kickboxer Kickboxer wrote:

I'm going to call "SHOOTER ERROR".  A few years ago, Richard Wild set a record using the March 8-80.  An Australian record, I believe, but a record none the less and nothing to laugh at or criticize.  I seriously doubt his ability to do that if there were a scope design flaw.
 
At 80x, sight picture/cheek weld is CRITICAL.  Consistent, exact placement is mandatory.  Your exit pupil at that power in that scope is 0.7.  Highly subject to parallax error.  What you need is a 160mm objective...
 
I just looked it up... he shot a 2.067inch group at 1000 yards with the March 8-80... set at 80x.  Not bad, not bad at all...
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/05/2013 at 22:05
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Overmagnification leads to overaiming and overcorrection by the shooter.
 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/05/2013 at 23:19
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Hi Kickboxer,
Your logic makes sense. The pattern is inconsistent at high power so I guess the hold is more critical than we could have imagined.

That Australian record is less than 0.25 MOA without any wind factor. It is remarkable and it was results like that which helped my decision to buy the March.

How or where do we learn more about the critical aspects of consistent hold particularly at high power?


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/06/2013 at 03:50
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Try these for information...
 
 
I believe parallax is your big problem... you have to spend a lot of time learning to overcome yourself at "high power".  Being able to position precisely is a difficult skill.
 
Welcome to OT.  There are some very good shooters here who can give you very good instruction. 
 
 
 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/06/2013 at 10:42
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Another factor is over compensation. The movements associated with hand eye compensation are exaggerated with magnification. Movements are easier to control up to around 16X for most people. After this level it is much harder for the brain to control the smaller level of movements. This in more likely due to lack of time using the higher magnification, allowing the brain to learn such fine movements. When you take the magnification away from the eye, your brain  readjust to normal reaction speed. When going back onto the scope, the drastic reaction speeds have to be reacquired. It takes much longer to get the body to adjust to the high magnification than needed for lower magnification. The time frame for the shot pictures usually will not last long enough for the body to fully adjust for the higher levels of reaction adjustment change.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/06/2013 at 10:47
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Off topic but this comes to mind.

http://www.youtube.com/watch?v=V2i8eZBqC3A

Because I have one...  200-300-500 (come on that is 6x range)...



I might chime in on this one and state that at higher power you should loose no accuracy and gain precession.  Your factor of and field of view becomes that your margin of error becomes much smaller with your correction your point of reference becomes smaller and your correction should decrease your POA vs your perceived POA. 

Some say that they need spacial bounds or area outside of the target to shoot more precise.  Your groups should not open up due to magnification alone but maybe it is in your best to keep a lower mag range than say go to 80x.  I would think that the bounce and roll and throb would get you at 80x I hope this is all prone or bench I am getting cramps thinking about it...

I have never had the pleasure of owning a march but would love to shoot 35-80x with it mind you i doubt that will ever happen but it would be neat for the 1-2 mile shots.

What are your groups at say 20x, 40x, 80x...

What is your sway??? How far off do you drift or breath?  In inches??? what pattern???

I think your test should be at 500 that way you still have some FOV.  Mind you it will be under a few feet...

Each shooter learns long distance differently some have bad tendancies by marksmanship shooter standards but pull off incredible feats.  I like to chew bubble gum and use it as a cheek rest and breath through shots but some believe a breath out should be given, old school says hold...

I know for me to practice without wasting money is just plink 22lr at 200yards trying to see what my issues are and work them out.   I go through seasons if you will of bad habits especially the more I get out of shape...

One thing is true you can never learn enough or have enough rounds downrange you continue to learn even if to your discredit.


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/06/2013 at 13:41
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Thanks for all the feedback. I should clarify this rifle is 10kgs and shot from a bench or the ground on stands that allow absolutely rock steady aim at any power. The trigger is approx 4oz. so doubtful if the release is causing errors.

The scope is on this website and the reticle I use is in the top row in 3/32 dot http://marchscopes.com/tactical-8-80-x-56.html. Other stats, the calibre is 6.5 x 284, barrel 32" 30mm dia, velocity 2950 +/- 7ES with 139gr Lapua Scenar, ambient temperture range 16-24C, humidity range 70-95%. Should do one hole groups all day, but only once has it happened. 

In view of some comments regarding parallax, I am reviewing my records and it appears the groups were better in the winter. Therein maybe a clue with hotter weather here now bringing the mirage factor and/or rise in humidity into the equation. High magnification exaggerating the mirage and making precise parallax adjustment impossible. Focus maybe clear, but it is impossible to test for cross hair movement on an image that is bouncing. What is the answer?

I just love the bubble gum trick thanks for that




Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/06/2013 at 15:11
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Well everything seems good but you.  Wink

Just joking but all in all it seems like you have a tremendous setup that should pull off some nice groups.

I am wondering if it is Barrel Mirage and Barrel Heat not just magnification.  Do you use a mirage band or deflector???

Not just distance mirage but rather heat from barrel has caused me some stress.

Also note that the higher the mag range the worse anything will be for what you are noticing...

Maybe it is the scope send it to the USA and we will test it then send back...Cool
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/06/2013 at 19:43
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Optics GrassHopper
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I have some venetian blind louvres ready to install over the barrel. What was your experience? 

This is intriguing, because recently I shot my first one hole 3 shot group from a cold barrel that was so unbelievable I had to walk downrange to inspect it. I am wondering what happened during this time because the next two shots when I returned were 0.25" away from that hole and not together.  

I doubt the barrel would have heated enough to warp, but it may have become hot enough to exacerbate the mirage......good point thank you. The louvres will be on next time I shoot.

Thanks for your kind offer to test my scope, but methinks this is only going to happen when you are at my range in NZ.........and maybe Clown 


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/06/2013 at 21:00
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If you have never seen this than I would try to go shopping they are readily available this is a very well known phenomenon.

I prefer the fabric kind that go over the front sight or muzzle brake screw if your brake does not have one drill and tap your own.

Do not try to make this your self you will be displeased some people go to the local fabric store and try to assemble them.

The proper mirage band has tension to it does not blow in the wind and stays fixed to the gun while shooting and while in storage.

It should be of a material that can get wet and that can dry easily.  It should be non reflective in nature and porous.

For those that have never let the barrel get that hot well keep shooting slowly and enjoy.

The barrel itself does not warp from what I have seen in a bolt gun a Full Auto gun yes but not bolt gun, at least the cold hammer forged and cyro barrels I have used...

I need to learn how to shoot that slow, I still am quick to follow up and just can't kick the habit.

My loads are such that most of them are not barrel burners but have lots of pressure and lots of heat.

I am not exactly sure of your issue yet but as your rifle barrel gets warmer and if you can keep it hot specifically you will be able to group tighter and the longer it is hot the longer you will be in the zone long distance shooting is not a 10 second sport in my opinion unless you are  trying for cold barrel shots or have some club rule against it.

I tend to think that the walk downrange caused your .25 and that you will start to note that the longer you wait the further off you will find yourself.  If you can keep stringing groups you will find you can maintain a greater accuracy/precision factor... The problem with most shooters is breathing and 2nd nature of loading and bolt work, not when she is feeding but when you run into issues with keeping her fed and happy, one mistake in this task and your "score" could be ruined.


I am a firm believer in learning how to deliver many shots in a bolt gun very precisely.  Follow Up on many targets is not something to take lightly. When the Zombies as you call them attack and you they are at a distance I would prefer a bolt gun due to inherent accuracy.

For your style of shooting I suggest getting this guys system to work for you.

http://www.youtube.com/watch?v=03qtXpoObfM

Target Blind...

What a horrible group...

He is pulling them .25 just like you...His aren't together either.

Back to normal rifles and setups.

Mirage bands can be very useful when your scope over bore is low.


It is impossible to figure out what your issue is but something to consider.



  
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/07/2013 at 03:43
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I know Stuart, he has been at benchrest for over 30 yrs and he sold me the March.

He is very knowledgeable and very helpful as well. BRT also run courses on techniques, wind, loading etc so if I can learn as much as you guys, then take a course with BRT the issues will probably resolve themselves.

I see Stuart has nothing on the barrel of his, but he will where the band can be obtained. I have heard of them, but never seen them. 

Thank you 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/07/2013 at 07:44
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http://www.accuracyinternational.com/accessories_list.php#15

Probably the easiest to get your hands on.

I saw a few .nz sights that sold AI...
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/09/2013 at 13:41
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Thanks again guys. I found this article by Ilya Koshkin (http://www.rimfirebenchrest.com/articles/parallax.html) There is enlightening information there regarding the reticle focus as a factor in parallax error and also the error is in direct proportion to the magnification ie at 9x is it three times greater than 3x. Our magnification is as much as 80x so I get the picture.

This may explain why our  groups are better at low power than high power.

The error is most likely there because of the mirage from both barrel heat and ground moisture, making focus and reticle movement impossible to accurately remove, combined with our old eyes, standard prescription glass lenses, instead of custom fitted shooting glasses.

One question remains, how is it best to eliminate parallax error when a mirage is running?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/09/2013 at 19:37
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That article talks about scopes without an AO or SF. Doesn't your March have an AO?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/09/2013 at 22:49
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The scope has all the bells and whistles inc SF, but in a mirage which we have constantly now except when the wind is over 12mph of course, the target image is all over the place, jumping up and down and sideways, and also goes clear and fuzzy, all at the same time. 

The humidity approaches 100% with 30C temperatures here in NZ this summer making focusing in my opinion impossible, that is of course if I am trying to focus on a target image. Is there any other way? 


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