F Class Accuracy - What is required to win ?

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plumbs7
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Re: F Class Accuracy - What is required to win ?

#16 Postby plumbs7 » Mon Jun 20, 2016 6:58 pm

RAVEN wrote:IMO

A rifle load combo that averages .3moa is usually good enough to win most competitions
chasing the holy grail can be fun but it’s about return on effort.
no point in tuning a gun to shoot in the ones if you can't read the wind and frankly a lot of rifle just aren’t capable of this higher level of consistent accuracy
RB
P.S the groups size focus is on vertical
any horizontal stringing is very hard to determine unless you shoot in a warehouse or tunnel and I know there aren't too many of those available.
so stop chasing the holy grail and get shooting competing will teach you more than posting 3 or 5 shot groups on the internet.

Ouch ! That hurt ! :cry: lol!

RAVEN
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Re: F Class Accuracy - What is required to win ?

#17 Postby RAVEN » Mon Jun 20, 2016 7:07 pm

Keith one of the things that I have notice is some newer ppl to this sport focus on the wrong things instead of taking an overall view.
When I group test I look for a low SD of group so a greater percentage of shot in theory should hit the X ring.
Reality is different.

I call this the reality check sometimes expectation do not coincide with reality.
or ppl are trying to achieve an unrealistic result think that once the holy grail has been achieved the bullet will automatically be draw to the X ring
The mind set of one’s game plan can get results if the marksman has confidence in their load development they can then just concentrate on the wind
and this is very important in being consistently competitive.

RB :)

plumbs7
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Re: F Class Accuracy - What is required to win ?

#18 Postby plumbs7 » Tue Jun 21, 2016 8:10 am

Totally agree Richard . There has to be a balance and at the end of the day one must put it in the middle of they can ! :)

KHGS
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Re: F Class Accuracy - What is required to win ?

#19 Postby KHGS » Tue Jun 21, 2016 10:17 am

RAVEN wrote:Keith one of the things that I have notice is some newer ppl to this sport focus on the wrong things instead of taking an overall view.
When I group test I look for a low SD of group so a greater percentage of shot in theory should hit the X ring.
Reality is different.

I call this the reality check sometimes expectation do not coincide with reality.
or ppl are trying to achieve an unrealistic result think that once the holy grail has been achieved the bullet will automatically be draw to the X ring
The mind set of one’s game plan can get results if the marksman has confidence in their load development they can then just concentrate on the wind
and this is very important in being consistently competitive.

RB :)


I would agree 100% with you Richard. Unrealistic velocities, unrealistic SD figures & unrealistic group sizes. Sample size has been mentioned on this board, this needs to be taken into consideration when analysing data. Very often we will latch onto what we want to see, enter that word "unrealistic" again. A small 5 shot group does not mean that your rifle is agging that group size. A small string in a velocity check giving a low SD does not mean all strings will have the same low SD. So we take all these as "indicators" & test on the range in club shoots to prove performance consistency. One small group with low SD means nothing if the rifle can't consistently produce those results. Many times a small sacrifice in group size & or a small sacrifice in SD will produce a more reliable result overall. Thats a bit longwinded for me "phew". 8)
Keith H.

Norm
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Re: F Class Accuracy - What is required to win ?

#20 Postby Norm » Tue Jun 21, 2016 10:50 am

I find the "Ontarget" software handy in interpreting the accuracy potential of loads.
It gives an ATC feature. "Average to Centre".

So you can fire a number of groups with the one load either on paper targets or electronic targets. Then compare what the average distance of each shot is from the centre of each group. These can be compiled and a SD type figure can be developed for that load over a period of time either from groups shooting or from the results obtained using electronic targets during competition etc.

With this you can compare various loads to see just which load gives the more consistent results.

This is a totally different way of comparing loads compared to the traditional way of just looking at group size.

williada
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Re: F Class Accuracy - What is required to win ?

#21 Postby williada » Wed Jun 22, 2016 6:43 pm

Few people have put a great amount of shots down the range at 1000 yards from a machine rest with a seriously large sample size over different seasons and years. That range is special and on the margins of ballistic performance which absolutely tests the normal distribution models. Absolutely you need a tuned rifle capable of small groups to improve score.

What I discovered was the group shape changed in winds over 10 m.p.h. became elliptical and their axis was also linked to muzzle timing, was more pronounced with left wind, that right winds produced tighter groups and how critical small velocity changes were in regard to your twist rate and group size. This is very close to when mirage is blown away, so you have to be careful to discount that if you are not using a machine rest. There were quite a few other findings that I will reserve for development programs because they depend on developing people’s understanding and cannot be given justice to in these threads trying to bring some folks up to speed. Just as when you first start shooting you have to learn to read wind, there are advanced lessons to be learned when you have mastered the basics.

Granted a computer model can impute changes to a very small degree that humans could not even visualise and that is a problem for most. We have to deal with the actual. In that sense, the ellipses are skewed. You have to then ask yourself then, how applicable is a standard deviation of velocity to a skewed distribution with what you are testing? You can shoot hundreds of shots and the skewed results will pop up due to conditions we have no control over.

My solution has been to reverse engineer from the groups on the target. Some groups such as a competitive shoot are small compared to a significant sample from a test I have done, but my thinking is based on the large sample. When I overlay many smaller groups, I soon see the trends. Just as cross checks do with other tests.

A casual glance at a small group in isolation is meaningless unless you see the whole process. Just like the advice Matt received regarding SD numbers on a 10 shot group from Dave, but his thinking like mine was based on larger numbers with tuned rifles. Similarly, computer models not based on tuned rifle parameters are meaningless and random because of course you can hide sections of the whole spread to look like small groups and then show the big picture to reveal it’s not small it is huge. That does not represent a tuned rifle but is selling a concept that you have to be aware of before refinement can be made for judgement. It is also the same conceptual process the university teachers on .248Win’s You Tube link did describing Magnus force and gyroscopic force on the ES SD thread did. It does not quite happen like that in reality with projectiles. Teachers do this, then in the next stage they would introduce high order analysis and synthesis skills to refine and make judgements. It’s about getting the idea first. The thing you need to do is to see if the groups are repeatable if they are small.

My solution to short range testing, where we can produce normal distributions easily, raises another problem i.e. finding the tune from which we can draw comparisons for normal distributions. Normal distributions have outliers we classify as random. But if we have enough knowledge we can find causes of the outlier and where possible reduce its impact to find a tune. I do that by examining frequencies and harmonics to identify different frequency paths including group centres and over time I have discovered causes. There are a few people in Qld, who sent me groups through the development process where I was able to identify the problem and fix it. The methodology has not been made public and only a few have been exposed to it with great success. I dare say others will improve on it as we have built on other people’s work.

Many groups of significant sample size remain skewed at long range and it is due to a greater influence of the Magnus force at the over tuning point and way down the track with constantly changing centre of pressure which also contributes to greater yaw of repose, of which spin drift yaw is a part. Two uneven forces one vertical and one lateral will form an ellipse. The Magnus force although small is linked to vertical and the spin drift has greater links to the lateral but remains fairly constant, the Magnus force does not. Pulses are set up which tend to cluster shots and disperse others by tiny amounts. If your velocity is not matched perfectly to the twist rate these groups will be bigger, so the timing of bullet nose oscillation as it hits the target can change impact point significantly at long range. We cannot see this minor, but still significant stuff in conditions.

Being truthful who can read wind to 2 mph and account for different wind zones over 1000 yards or different air densities regularly, which are affecting the centre of pressure on the bullet? We can measure it on the target and take note that in these general situations, particularly with a left wind over 10 m.p.h. an ellipse will form. Or if it’s too big there is a velocity issue. Frankly, you have to learn to master a big group at 1000 yards as Tony was demonstrating. You have not got much to play with if your group size averages ¾ minute. That’s a 1/8 either side as buffer. That margin can be enhanced knowing your group shape. The hardest part is seeing that ellipse in all the shots if your sight are moved based on position as well as wind. That is the art of reading the tea leaves.

Why wouldn’t you centre your group properly based on an ellipse when taking wind changes into account? This is about getting to know what to look for, not reading something into it; what your rifle will do and that is different to what it does at short range compared to long range. That means also taking into account a barrel’s compensation profile or a mechanical or tuning issue that loses odd shots. Still the ellipse will underpin it whether large or small at 1000 yards if winds are greater than 10 m.p.h. It is a coaching issue. Many people have just learned what the actual apparent aiming mark movements do too, and they will benefit by applying this knowledge. Surely you would want to know if you are winding the sight the right way.

The Project Penumbra and extensive work over 5 years in the 1980’s did determine the right twist rate and bore size for .308 with factory and reloaded ammunition for the Sierra 155. This examined not only static gyroscopic stability which most texts refer too, but considerable work with dynamic stability which relates to yaw of repose which relates to centre of pressure and centre of gravity with Magnus force and gyroscopic spin. Of course the different twist rates we used in paired barrels determined the tractability i.e. the ability to stay on the bending trajectory path. There were also experiments with transient yaw that dampens with distance such as nutation (javelin –like wobble) and coning to find that 140 yards was a suitable test distance. This was produced before a paper was written in America confirming the procedure that Norm supplied me with.

Graham Mincham also confirmed with me in discussion and in writing in 2002 that led me to conclude there should be different barrels matched to different distances in terms of dynamic stability and tractability. This is why we tested paired barrels from 1-12 to 1-15 with different bore sizes.

Finally, while a tuned rifle with low angular spread at short range is a great all rounder, that 1000 yards is special and on the margins. However, a one rifle setup limits the scope setup. By that I mean you are disadvantaged by not having the optical centre set for 1000 yards. This adds a real problem when you want to reduce parallax errors which you can detect by moving your head up and down, left and right. With a scope set for 1000 yards it is less likely to run out of windage and not develop erector tube problems because the internal springs have not been cramped. I have seen scopes suddenly bugger up in the VRA team championships in successive years and would you believe my old Nightforce has just done that because I have to screw down to 300 yards and cramp that spring. We don’t have much long range shooting in my current club.

Anyway those have been my experiences for better or worse that have shaped my thinking. I always stand to be corrected. David.

Chopper
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Re: F Class Accuracy - What is required to win ?

#22 Postby Chopper » Wed Jun 22, 2016 7:37 pm

Wow, can I start to reply from the top ,? what type of machine rest ?, Chop

williada
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Re: F Class Accuracy - What is required to win ?

#23 Postby williada » Thu Jun 23, 2016 12:03 pm

Made a few Chopper, all shapes and monsters, but they were all return to battery rests. If you every get admitted to the Winchester underground testing facility they have a massive return to battery rest. I mean massive! The cradle is the size of two Cummins diesel heads.

When I was young, I copied Fulton’s rest which allowed the rifle to recoil with great freedom. Forward and aft, left and right, and up and down as it sat between two V blocks. A very sneaky design you do not notice unless you realize why the register point is on the trigger guard and to one side of the trigger guard for good reason. This one taught me a lot about compensation. None of these rests were meant to be one holers, although some were bloody tight and produce groups under one minute at 1000 yards in the right conditions, otherwise you have to discount wind factors to evaluate real group capability. They were designed to show the relative difference in components, whether that be muzzle weights, position or ammunition. They had to be tuned, which I will talk about shortly and people do not realize that.

The last one I used was professionally built and came in two dismountable parts for the NRAA testing. The stand was the Fulton tripod so it could be used in the field at different ranges and to do pressure testing so I did not have to bend my back as the testing took all day and months of it switching many paired barrels. Corby lent me his Border pressure tester but I could not use it with this configuration, with the infra red temperature barrel monitor and chronograph while pointing it at a target to give me relative readings in groups. I could with the Pressure Trace system.

However, the rest could be taken off this finicky stand (still accurate if still set up properly on small concrete pads) and be placed on a heavy concrete surface like a rail gun being supported by three pins for the real business. The base was very heavy and the mid section could be adjusted for elevation and windage to get on the plate at 1000 yards then locked down.

This rest was designed to allow the sliding section to mimic a prone shooter. It was comparable to a shooter shooting alongside it but it could hold a tighter repeatable group than a shooter all day once tuned and set up. The weight of the sliding section was based on calculated recoil into the shoulder, so it did not have the mass of a Winchester setup for good reason as I had learned from my Fulton rest. The cradle slid back on V blocks and was free to lift up. The tune was controlled by moving weights in the horizontal and in the vertical that could be positioned above and below bore-line as a lot of discussion I introduced on stock design came from those experiences.

A block on top of the cradle was specifically designed to hold an RPA action not the barrel, so I could switch barrels in a controlled way to compare them -all easily doable on the range. It was boxed up and sent to NRAA when I was finished with it with a number of universal throat reamers which allowed me to test leed angles, the test barrels and scope that were not mine. I believe the barrels went to Winchester to use in their test facility that represented the stuff we use rather than their short light test barrels that sporters use. I think this added to quality testing of ammunition that they provided all Palma shooters across Australia with. Those that have the machine rest now, would not know how to tune as Pearcey verified, and that it had to be separated from the stand to be placed on a heavy base of concrete for very accurate results. It would shoot under a minute all day at 1000 yards in the right conditions once sighted in and the cradle could be moved to swap barrels and be replaced in exactly the same position.

On one occasion there was a penicillin moment of discovery, when I first shot the thing at home in terms of compensation. When doing leed angle tests, I had a bunch of rounds giving me an extreme spread of 60 + fps. At short range the bastards practically just opened up one hole - a thirty-five inch barrel doing this? It was repeatable, and I have posed card a while back. This should not happen. I took the gear apart and discovered only the rear recoil plate on the action was touching. I showed it to Pearcey. Although still held by the take-down screws, like a No. 4 on the rear draws, the barrel was effectively made longer, and so was thefundamental sine wave for length for tune. It also showed me a barrel could be made to compensate at very short range. It made me watchful and not to be fooled by tight groups up short that would not repeat out long. After the key testing was done, I had a play with barrel lengths and my own barrels as I had a supply left over from 1980’s work and again as I did in the past by cutting them down.

A machine rest makes this so much more objective. David.
Last edited by williada on Thu Jun 23, 2016 5:06 pm, edited 2 times in total.

williada
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Re: F Class Accuracy - What is required to win ?

#24 Postby williada » Thu Jun 23, 2016 4:39 pm

Scanned an old paper.

Image


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