tricks to achieve low es??

[Cool Tool]

Standard deviation is a statistic that measures one important characteristic of a normal distribution, which is also known as a “bell-shaped curve.” The assumption that we're dealing with a normal distribution is important for calculation of sd, and velocity data do seem to follow a normal distribution. I've tested a number of sets of data from chronographs which did in fact approximate a normal curve (i.e., were not significantly different from normal), so I’m sure that the algorithm for calculation of sd that’s programmed into the chronograph makes that assumption. (Lest someone jump in to point it out, I’m aware that velocity is a vector quantity, so what we’re really talking about is speed, which is a scalar – but velocity seems to be the term in common use, so that’s what I’m using).

So, the chronograph uses the individual velocity readings to calculate the mean (average) velocity and then looks at the deviation from that mean of each of the individual data points to calculate the standard deviation using a formula that is not greatly complicated but which we don’t need to get into. A small standard deviation indicates that the data points are clustered more closely around the mean, while a larger sd indicates more spread, i.e., more variability. Because consistency in velocity for the individual shots of a particular load recipe is [presumably] conducive to greater accuracy (precision, really), a smaller sd is always (I think) better, but it’s also important to consider the size of the mean velocity in question – for example, an sd of 20 for a set of low-power pistol loads that have a mean velocity of 700 fps is actually indicative of greater relative variability than an sd of 30 for high-speed rifle loads that average 3500 fps. The statistic that takes that relationship into consideration is known as the “coefficient of variation” (abbreviated CV, and also known as Relative Standard Deviation, RSD), which is simply the standard deviation divided by the mean. In the first (pistol) case the CV is 20/700 = 0.029 (and usually given as a percentage, so 2.9%), while in the second (rifle) example, it’s 30/3500 = 0.009 (0.9%), so the rifle data are actually more consistent, relative to the larger size of the mean.
the sd can be used to determine the percentage of your shots that you can expect to fall within a certain velocity range. For any normal distribution, the mean +/- one standard deviation will include about two-thirds of the data points (68%, in fact), +/- two sd will include about 95%, and +/- 3 sd over 99%. Using the rifle example, with a mean of 3500 fps and an sd of 30, 68% of all shots taken with that load (all other factors also being equal) would be expected to range from 3470 to 3530 fps, 95% should fall between 3440 and 3560, and over 99% would be between 3410 and 3590. Another way to look at the same numbers would be (for example) to conclude that only 5% of the shots would either be slower than 3440 or faster than 3560 fps.

The question of how many shots in a data set are necessary for calculation of a “meaningful” sd can be approached by considering the Student’s t-distribution in comparison to the normal distribution. The t-distribution is, in effect, a normal distribution that is mathematically adjusted to account for a small sample size. The amount of the “adjustment” for a particular small sample size is a measure of the uncertainty relative to having lots of data. In a normal distribution, based on an infinite number of data, +/- 1.96 sd includes exactly 95% of the data points. If, for example, you had only 20 data points (e.g., a string of 20 shots) the t-distribution says you would have to increase the 1.96 to +/- 2.093 sd to be confident that 95% of the data are included – the range is greater because of the uncertainty arising from the small sample size. That amounts to a difference of (2.093 – 1.96)/1.96 = about 6.8%, which is probably close enough for the average person evaluating loads but probably not, as steveno points out, good enough for a manufacturer. By the time you get down to a 10-shot string, the difference grows to about 15%, and for the typical 5-shot string, the difference is a good bit larger – nearly 42%, which I think makes a pretty good argument that sd based on a 5-shot string is a suspect value that should be used only with caution, or not at all.

Thanks makes sense now.

 

[Terry]

WEll now that someone give a answer which is the best to tune by honestly thanks.

Perhaps we are focusing on the wrong thing.

BR shooters want small groups. F-Class shooters want minimal vertical.
While ES and SD are part of it, it's what shows on paper in the end.

 

[JamesnTN]

WEll now that someone give a answer which is the best to tune by honestly thanks.

I go by what the target tells me the rifle likes

 

[savagedasher]

BR shooters do It all the time.
If you have watch them you would see .
They do It without thinking .
How many of time have you watch them through a case away or not use it again . They are sorting on paper because of vertical . Larry

 

[Joe R]

Okay guys I need your help!!! I have tried and tried to get my extreme spread down in the single digits and I can not obtain what I want. Usually my extreme spread on my guns is between 15-30 mostly in the upper 20s though. I'm looking for the tricks of the trade from those of you that can achieve low es with quite abit regularity. What method do you use to weigh powder charges, and what equipment? How do you get a consistent over length every time on loaded ammo? How do you get consistent neck tension? Do you weight sort all bullets you shoot and measure them from base to ogive even when you are using high quality long range bullets? Also any other important factor you have learned that helps I would be interested in hearing.

Like many people have already stated the answer to: "important factor you have learned" is everything matters. Like they used to say in school "a line can be broken in infinite number of points", so can the process of reloading for precision ammo.

To help you focus here's what EriK Cortina once told me: "The Holy Trinity of precision reloading are:

1. Powder
2. Seating depth
3. Neck tension "

The first two are pretty straight forward, the neck tension is the hardest nut to crack. Annealing every time is one of the main tools used towards the goal of getting consistent neck tension, but there are many others needed to crack that nut. Here is a thread discussing one of the tools my gunsmith invented for me that has helped http://forum.accurateshooter.com/threads/the-ultimate-solution-to-neck-tension.3909740/

Kindest regards,

Joe

 

[RonAKA]

The first two are pretty straight forward, the neck tension is the hardest nut to crack. Annealing every time is one of the main tools used towards the goal of getting consistent neck tension, but there are many others needed to crack that nut.

I recently did some testing on using different annealing temperatures. I would suggest that the annealing temperature and time used is the biggest factor in determining neck tension, not the actual interference fit that we can easily measure. The reason is that the fit is less critical is because the brass yields when the bullet is fitted more than a thou. That tends to blunt any differences in fit.

However, the yield point is greatly affected by annealing temperature and time. Without getting into details. I compared the seating force of a worked but un-annealed to three other cases that had been annealed at different temperatures. Here is how the force compared:

1. Un-Annealed - 18
2. Lower anneal - 9
3. Medium anneal - 6
4. Higher anneal - 4

So annealing is critical for uniform seating force. Annealing every time is a good start but then uniformity totally depends on your uniformity of annealing.

 

[ab_bentley]

I recently did some testing on using different annealing temperatures. I would suggest that the annealing temperature and time used is the biggest factor in determining neck tension, not the actual interference fit that we can easily measure. The reason is that the fit is less critical is because the brass yields when the bullet is fitted more than a thou. That tends to blunt any differences in fit.

However, the yield point is greatly affected by annealing temperature and time. Without getting into details. I compared the seating force of a worked but un-annealed to three other cases that had been annealed at different temperatures. Here is how the force compared:

1. Un-Annealed - 18
2. Lower anneal - 9
3. Medium anneal - 6
4. Higher anneal - 4

So annealing is critical for uniform seating force. Annealing every time is a good start but then uniformity totally depends on your uniformity of annealing.

To add to this, neck cleanliness is a item of interest. I've stopped annealing but started cleaning the case necks with a bore brush. The same ES/ SD came into play with the change of the procedure. If no annealing and no cleaning took place, ED/SD doubled or tripled. Leading back to the seating force being critical role in the low digit game.

 

[Terry]

I recently did some testing on using different annealing temperatures. I would suggest that the annealing temperature and time used is the biggest factor in determining neck tension, not the actual interference fit that we can easily measure. The reason is that the fit is less critical is because the brass yields when the bullet is fitted more than a thou. That tends to blunt any differences in fit.

However, the yield point is greatly affected by annealing temperature and time. Without getting into details. I compared the seating force of a worked but un-annealed to three other cases that had been annealed at different temperatures. Here is how the force compared:

1. Un-Annealed - 18
2. Lower anneal - 9
3. Medium anneal - 6
4. Higher anneal - 4

So annealing is critical for uniform seating force. Annealing every time is a good start but then uniformity totally depends on your uniformity of annealing.

With all due respect, you either reach the temperature that changes the brass or you don't. Less = no change, More burns out some elements of brass.

 

[ngb1787]

If this helps we are also running a mandrel thru necks after sizing, this opens up to a lighter seating. Uniform tension.

 

[expiper]

use max loads,,,,the powder does not burn rite if you are running with the choke pulled,,,you will never get rid of verticle running mild loads,,,,Roger

 

[Cool Tool]

use max loads,,,,the powder does not burn rite if you are running with the choke pulled,,,you will never get rid of verticle running mild loads,,,,Roger

That's interesting please elaborate on that please.

 

[RonAKA]

With all due respect, you either reach the temperature that changes the brass or you don't. Less = no change, More burns out some elements of brass.

Sorry, but I beg to differ on that. Do you know that during the manufacture of brass the brass is heated to over 1100 deg. F, at least a couple of times? That is the whole cartridge. The better brass has the neck and shoulder only annealed last. If high temperature burned out the elements of the brass they would have been long burned out in the factory before you ever got the case. The common belief that if you heat brass to too high a temperature, that it is ruined for life, is basically a myth. If you melt it, it just changes the start over point.

Here is a a graph on how the hardness changes with temperature and time. Yes, if you don't get the brass up to the 800 F range not much happens. But beyond that you can reduce brass hardness and thus yield over a wide range. Annealing is a little more complicated than it first may appear to be.

 

[Terry]

Sorry, but I beg to differ on that. Do you know that during the manufacture of brass the brass is heated to over 1100 deg. F, at least a couple of times? That is the whole cartridge. The better brass has the neck and shoulder only annealed last. If high temperature burned out the elements of the brass they would have been long burned out in the factory before you ever got the case. The common belief that if you heat brass to too high a temperature, that it is ruined for life, is basically a myth. If you melt it, it just changes the start over point.



Here is a a graph on how the hardness changes with temperature and time. Yes, if you don't get the brass up to the 800 F range not much happens. But beyond that you can reduce brass hardness and thus yield over a wide range. Annealing is a little more complicated than it first may appear to be.

Their is no 800 on your chart. I do see change at 400-500 though.

 

[savagedasher]

I recently did some testing on using different annealing temperatures. I would suggest that the annealing temperature and time used is the biggest factor in determining neck tension, not the actual interference fit that we can easily measure. The reason is that the fit is less critical is because the brass yields when the bullet is fitted more than a thou. That tends to blunt any differences in fit.

However, the yield point is greatly affected by annealing temperature and time. Without getting into details. I compared the seating force of a worked but un-annealed to three other cases that had been annealed at different temperatures. Here is how the force compared:

1. Un-Annealed - 18
2. Lower anneal - 9
3. Medium anneal - 6
4. Higher anneal - 4

So annealing is critical for uniform seating force. Annealing every time is a good start but then uniformity totally depends on your uniformity of annealing.

I have a question is the seating force or is the flex of the shoulder. My belief it is more the shoulder. Larry

 

[majohnson]

For those of you that have not read Litz last book there is a chapter that goes over this topic that add some fact to what we think about reloading, and annealing case.

 

[Cool Tool]

Sorry, but I beg to differ on that. Do you know that during the manufacture of brass the brass is heated to over 1100 deg. F, at least a couple of times? That is the whole cartridge. The better brass has the neck and shoulder only annealed last. If high temperature burned out the elements of the brass they would have been long burned out in the factory before you ever got the case. The common belief that if you heat brass to too high a temperature, that it is ruined for life, is basically a myth. If you melt it, it just changes the start over point.

Here is a a graph on how the hardness changes with temperature and time. Yes, if you don't get the brass up to the 800 F range not much happens. But beyond that you can reduce brass hardness and thus yield over a wide range. Annealing is a little more complicated than it first may appear to be.

What I think would be really interesting is that seating pressure you achieved on brass annealed at certain temps do about 25 pieces of brass seat 5 today write down the seating pressure on your gauge wait 2 days seat 5 more wait 2 days seat another 5 write the seating pressure down each time I would be willing to bet it will change dramatically it would be interesting what you find.

 

[Mulligan]

Their is no 800 on your chart. I do see change at 400-500 though.

.

800*F~426*C.
Two units of measure in the info provided
CW[/QUOTE]

 

[SheepDog]

I'm not sure that a couple of days would change the force required to seat a bullet in an annealed case but if you spread it out over months and years it will definitely change. Brass age hardens just as it work hardens, only less.

 

[dkhunt14]

I'm not sure that a couple of days would change the force required to seat a bullet in an annealed case but if you spread it out over months and years it will definitely change. Brass age hardens just as it work hardens, only less.

Brass does not age harden. MATT

 

[dcali]

The context for this is F class, where it's very relevant - it probably doesn't apply to benchrest, or at least it does differently. That said...

The trouble with using too many shots to measure SD is that the mean value changes as the barrel heats up. I've found that over a long string (like a typical F class relay of 22 shots), the variability of the velocity tends to stay pretty constant, but the average value might increase by half that amount from first to last shot. (I typically get a 10ish ES for shorter strings, but see the mean velocity increases by at least 5 fps over 20 shots). So SD numbers for long strings are needlessly pessimistic.

The most useful way to do this is to just sit down and shoot a full 22 shots and chart the results in order with Excel. You will get a very good intuitive feel for both the variability of velocity and how it changes over the relay. You need to know both because the variability determines how much margin you have, and the change tells you how much you need to worry about adjusting your aim point as you shoot.

Also, try it including cold bore shots. That can be an eye-opener. My current rifle/load puts out significantly higher velocity from of a cold bore. Not sure why, but I no longer trust my first sighter as much as I used to.