OzFclass

Andrew, there lies another trade off and these are sufficient. The data points are based on five shot groups which I feel is a minimum to establish a tune area for a baseline. Then you may move to smaller sample size with more incremental loads to increase your data points. By all means run with more 5 shot groups, but barrel life may become an issue when you need to do further refinements or test with a tuner to have the barrel in pristine condition for a big match. From a practical point of view, the fouling and heat issues sneak in and may not be representative of the match condition of the barrel. Very important. Another reason to check the visuals on paper to see if you need to explore further or maybe change components or setup if the best group size is not falling within an expectation fairly quickly. There are quite a few tangents to cover. But the methodology would be more precise with more data points, agreed. Of highest interest is the lowest point in the set.

Hi David,

A question you might care to have a go at answering.
It's always been considered that the point of minimum ES is a function of load Vs case capacity, but as seen in the curves, that of curve E has two values of minimum ES . One at about 51.5 gns and one at 58.5 gns. which begs the question " is case capacity the governing factor "
There are certainly other factors which come into play.
I have seen this many times with my 308's and it is repeatable so there is definitely something happening.
To my way of thinking case capacity has very little to do with ES --so what is it?

Barry, have a read on this site..... https://www.shootingsoftware.com/pressure.htm

Of particular interest is the secondary pressure waves that can occur with some loads. This could explain why you may get two loads with low ES that are a quite a bit apart.

Funny things happen when a cartridge goes bang.

[quote="Norm"]Barry, have a read on this site..... https://www.shootingsoftware.com/pressure.htm

Of particular interest is the secondary pressure waves that can occur with some loads. This could explain why you may get two loads with low ES that are a quite a bit apart.

Great website Norm. Ive never come across it before, thanks for sharing it.
]

Barry it is not absolute, you are right but it is a generalization which is mostly right going by observations. The examples we use fall into roughly the 90% range of one best load. High powder density with a suitable powder is safe and reliably produces great results. We have to look at sneaky fine tuning to take things further.

Like combustion engines if there is a fault you check fuel, air, spark and cylinder compression. Different combinations produce different efficiencies that sometimes pan out to be equal. On balance you would have to examine individual scenarios to be sure. But if you see the double header like the one from a QLD development member in 2014 the target probably has the answers which I will endeavour to describe shortly.

There are situations where lower powder density does work with a fast powder in terms of the case capacity and suitable bullet weight and there are situations such as we have experienced which influence the vibration pattern where I feel this phenomenon can be sourced at times.

I don’t think I know all the answers. Yes, I have used Pressure Trace since 2002, but I still keep coming back to paper punching because it is what I know and have associated patterns with Pressure Trace results, but I can honestly say I have not seen a secondary hump in the trace with the specific powders and the charges we use in this context. Perhaps it is not cold enough on rifle ranges in Australia to see the effect on slow burning powders and maybe the slow burning powders made here are not as temperature sensitive compared to powders made elsewhere to exacerbate these effects. However, the different powders do show up in group size and shape which I feel has more to do with vibrations and torque choking and expansion effects on a barrel. In some cases things balance out and in other cases problems are compounded.

A few experiences are worth recounting which may give us more insight. Boy, I wish they still manufactured 2206. Classic case of reaching maximum pressure close to the breech with standard throats with a load that did not fill the case in .308 with this fast burning powder, which tapered off well and where in the past, top scores could be produced with 144’s and 155’s.

Recently I posted on a compensation thread a preliminary test using a 7mm SAUM because I had extremely limited powder and projectile supplies. The case had considerable air gap when utilising a faster burning powder (2209) compared to what most used. (This is relative to the case design). I was confident I could find a spot where the combination of air and fuel could be married with a faster powder using a light 162 grain pill as we did with .308’s. I was confident it would generate a fundamental wave which I could work with to select a load. You have to expect erratic velocity behavior outside a suitable zone when you are playing with slightly larger air gaps not powder in such circumstances. I think this aspect makes many believe things are a bit unstable when it is not necessarily the case when you find a zone. Its a bit like being in the eye in a tornado.

Certainly the inexperienced have to be aware if they are experimenting with lower powder charge and larger air gaps than I use because it can be dangerous and you can get a re-ignition of powder in the wrong place. This would certainly show up in the second hump on a pressure trace if the gear survives. For insurance, I jammed the projectile into the lands with firm neck tension to ensure I had a complete burn and worked my way up in load by measuring the extractor groove with each shot for signs of high pressure. I am yet to take it for a full test due to lack of supplies.

So no, 100% powder density is not necessary but 100% powder density is very reliable and a safe procedure which I normally would recommend to others.

Today, top scores are produced with full cases of 2208 and mildly compressed loads of 2209 which are much slower powders than 2206, and used in stiffer barrels in .308 case design. These powders do perform well in hot conditions, but in Gippsland where it is cold 2206H has an edge in the .308.

It seems to me there is a separation of tune styles to control the muzzle i.e. stiffness V harmonics that is at play. In stiffer barrels, the lowest ES load is easily found and is probably related to the lack of torque choking and expansion in stiffer barrels. The beauty of the polynomial trend analysis is that it can give you a handle on three tune styles – nodal, OCW and compensation. Nodal tunes by definition are strictly velocity dependant, OCW require low SD’s to be effective at long range and compensation tunes require a nodal base to which it distances itself with expected ES.

Faster powders tend to give a full cycle of the fundamental wave at usable velocities compared to slow powders in the right barrel profile for you to tap into. Therefore, faster powder is more likely to generate an extra node of significance than a slow powder IMO.

Fast powder produces the higher order of vibration more readily, and it is used in harmonic tunes because it can dominate a tune. Slow powders on the other hand, tend to have lower order choppy waves because the stiff barrels are designed to control muzzle amplitude. So there is less emphasis on harmonic tuning in stiff barrels to find a natural spot in the barrel whip but the lower order harmonics which are subdivisions of the primary wave do exist to tap into. However, these vibrations are easily overridden at times by extraneous vibration, and reflected vibration or attachments to the system etc.

The interaction of lower order vibrations usually has distinct spread characteristics. This enables the polynomial ES trend to highlight the dominant harmonic node which is formed by several vibrations acting in harmony which are velocity dependent for use as a baseline. It happened in all situations and where there was one true node it was associated with the lowest ES and the best group on paper in pretty much the best position in terms of barrel lift in the polynomial trends we examined except for one. The double header Barry wanted to know more about produced two distinct areas for further exploration as determined by both group and ES. A bit like the true upper and lower node within the range examined but formed for different reasons.

It is complex at times. The plot in question was of a top QLD shooter back in 2014, using an offset stock from which we picked from the individual group patterns being thrown (very important near a tune area and a topic in itself) which was inducing and completing a cycle of key vibrations with the slower powder in this case. (If your stock design is not balanced you induce different vibration patterns. It can work for you or against you). This is not obvious in the 7mm’s with stiff tapered barrels and traditional stocks. Straight cylinder barrels have a better chance of producing this cycle.

When I viewed the targets which are not posted because others retain them as individuals in the development group, it could be seen the cycles of the primary vibration were more often incomplete and other vibrations were out of sync. As such, lower order harmonics formed the basis for fine tuning and the dominant tune area was more likely to show up with the low ES when several lower order vibrations were in harmony.

The case in point was revealing two areas of similar ES value, one happened to be at a trough on a secondary vibration and the other at the highest peak of both secondary and tertiary vibrations. Had the harmony of secondary and tertiary vibrations occurred at a lower speed, the groups would have been better as compared to the lower area where the secondary vibration dominated the tune and the tertiary vibration was working against it going in the other direction when we mapped them. I would expect an outlier to be caused by the out of sync tertiary vibration with a bigger sample at the lower velocity given this situation. Raw figures in isolation don’t tell you everything unless they have a context and of course the faster you go the percentage difference in the spreads is less. Holes in the paper will tell you what will be more reliable and where to look further IMO.

Hope I have given you something on which to build, Barry. David.

For guys that are not mathematically inclined, the following might save a bit of ammo if you do incremental load testing with an accurate chronograph, preferably not attached to the muzzle.

It is important to do a minimum of 5 shots per group in round robin style and waiting at least 45 seconds between shots so that fouling and heat variables can be accommodated. Preferably 5 x 6 groups so you build a significant sample.

Group patterns are not such a random thing. Group shapes and patterns can tell you a lot. Tight groups in a well balanced and armoured rifle are reliable. But in a rifle that suffers from problems, they will let you down sooner than later.

n.b. I edited and expanded on comments for the last graphic.

The examples above are situations that can occur, always look at what the groups are telling you. Low standard deviations of velocity with top draw ammunition is a primary goal and using polynomial trends with ES etc is just another indicator. Its not perfect but gets you close to a starting point. Rudimentary examination of vibration patterns is a pretty good backstop you can do on the spot.

Chronographs are not always accurate or placed at the wrong distance in front of the muzzle. Sometimes the figures are misleading. Its a good idea to use two chronographs for verification. Borrow the extra one.

Below is some testing we did with Ecomeat awhile back just to show how to broaden a tune. You can use more shots per group if you wish. We are really interested in the alignment of group centres to broaden a tune. If you want a tight tune that may fall outside these parameters, then make sure your SD's are low. Also note that less shots are required because we have already established the key middle load in the charge tests. Don't look at each group in isolation, the whole sheet is important.

After reading "the little blue book" I started load tuning for best ES with my new 284 WIN barrel a couple months ago. I did 6 round robin 5 shot groups with MagnetoSpeed on the barrel. Went home and did my sums and went back with the ideal load based on EXCEL with curve fitting and tuned the tuner for best group. This at 200 yd as I think this gives groups big enough to measure while still being close enough to minimize shooter errors? Then I fine tuned the barrel at 1000 yd for best compensation.
Now I have a 284 that will shoot as good as my 6BRX long range bench rest gun!

Normmatzen, you are switched on! I hope your nose and hands did not become blue coming out of the cold sifting through the series of small exchanges on this topic over time. My apologies for being cryptic at times, as us Aussies say, “don’t get led up a gum tree”. Has been a bit like, “Alice in Woderland” and pitched at a few audiences to get something out of it to give people access to knowledge - the purpose of course of the Little Blue Book you mention.

A few may not realise that Lewis Carroll who wrote that AIW about the 1860’s, was an English mathematician by the name of Charles Lutwidge Dodgson. His symbolism was unmistakeable and considered by a few to be a satire on mathematics. For example:

"Why, you might just as well say that 'I see what I eat' is the same thing as 'I eat what I see'!”
Believe your target.

Alice marvelled and noted that she has seen a cat without a grin, but never a grin without a cat.
Group patterns are not as random as you think, they happen for a reason.

She pondered the concept of “limit” when she was shrinking, having fallen down the rabbit hole whether she would go out like a candle.
I think we are approaching the limit of equipment but not the human ability to read conditions and choose an appropriate strategy to maximise results. We are still subject to the luck of the draw on the day.

When you change seats around a circular table you end up at the beginning.
May the best marksmen and women win, not the weaker competitors with better technology. When the playing field is level it will be the same as using issued ammunition. Hope they don’t change the rules like they did in a failed attempt to beat Walter Lindrum at billiards.

Below I post an excerpt of an old graphic I presented in 2003 to a TR Team at Bendigo, examining 10 shot groups in .010” sequences up to .100” (which I think I may have posted before). The label on the graphic needs correction. It should read Increasing Jump, which I did mention at the presentation at that time.

In essence, this graphic mapped the physical extreme spread of shots on the target to back up the chronograph readings. It was created at the time using the Excel graph feature of “Stocks” located under “More”. Haven’t tried this on new programs. ES methods have been reliable indicators over a long period for me.

We can still adjust tuners to be distance specific to tighten groups. In similar fashion, doing the seating depth test can put you in the same place if people do not possess a tuner. MS’s will work fine and find a good ES but they are of considerable weight and on removal may not give distance specific performance which of course using a variable tuner can then refine. The means does not necessarily justify the end.

Merry Xmas to you David, I need to find more time to read your posts, always enjoy them. Wishing you all the best for 2017.

Cheers
Danny

I've always been under the impression that to install a barrel tuner, after you have your powder weight sorted, would change the harmonics enough where evrything would all go to shit again (so to speak). But by finally getting the chance to read through this thread from start to finish, obviously I stand corrected. I must admit that I have never used a tuner myself, so it's never been a practical theory, just my own thoughts on harmonics.
So, in saying that this is now a changed thought, and as a target rifle shooter, am I under the correct thinking now that I could/should convert this to my front sight assembly? I'm sitting here waiting for my rifle to come back from the smith with a new barrel that I have asked for the recess for the front sight block to be cut longer, so I can adjust the block forward and backwards to fine tune my loads in the same manner that the guys used to do before we were aloud hand loads.
Now I can hear all you guys saying, "why bother, you're aloud 2moa for a bull." And you may be right, but if my rifle is capable of shooting 1/2moa and better with in it self, then the rest is all up to me to work on.

scott/r wrote:...Now I can hear all you guys saying, "why bother, you're aloud 2moa for a bull." And you may be right, but if my rifle is capable of shooting 1/2moa and better with in it self, then the rest is all up to me to work on.

That sort of statement is made quite often by F-Class shooters who I'm afraid to say don't know what they're talking about. In the same way that F-Classers go to great lengths to extract a poofteenth better accuracy out of there equipment, TR shooters will also benefit to some degree by improving every aspect. All else being equal, a TR shooter with only marginally better equipment accuracy will score better.

If I was shooting TR, it would have a scope rail on it, and a good part of testing would be done using a scope sight, and front and rear rests, to reduce sighting and holding errors and concentrate purely on rifle accuracy. Of course this isn't ideal, because both a scope and sling may affect harmonics, but unlikely to be enough to negate the benefits.

Danny, thank you, and I wish you every success in the coming year. Scott, keep chipping away, the sh%t turns to fertiliser and things will take off.

Budget, if you are reading Alan's words about putting on a scope to test TR equipment, they hit the nail on the head. Hopefully we have imparted a methodology.

David.