Spread Deviation Help

[Brux]

With my loads I am getting a maximum of 25FPS. How could I get these numbers down in the single digits?
308 sized with a Forster FL die
Berger bullets
Lapua Brass
Annealed every second firing
Trickle charge on a RCBS electronic scale that I check with my beam scale regularly
I use the die just like it came from Forster and I have measured the inside of my necks after sizing and I am getting 306

 

[usafa77]

Litz said in one book, if you load it to .1gr. tolerance and your sd is over 10, try changing primers. I have found a pretty wide range of sd's just by changing primer.

 

[Brux]

I'm loading to .1gr

 

[TripleBull]

Are you sure you are operating in a node? How long ago did you do load development? Did you optimize base-to-ogive ?

 

[Brux]

Yes,I have been doing load development for this rifle for the past 3 weeks and just finished up yesterday. I do measure base to ogive.

 

[lash]

When you say that you are getting a "maximum of 25 fps", are you talking extreme spread (ES) or standard deviation (SD)?

Because and ES of 25 is not bad, a SD of 25 could probably use some work.

[h=2]extreme spread[/h] [ek¦strēm ′spred]
(ordnance)
In a firing accuracy test, the distance between the two shots farthest from each other.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

[h=2]standard deviation[/h] (statistics)
(SD) A measure of the range of values in a set of numbers. Standard deviation is a statistic used as a measure of thedispersion or variation in a distribution, equal to the square root of the arithmetic mean of the squares of the deviations from the arithmetic mean.

The standard deviation of a random variable or list of numbers (the lowercase greek sigma) is the square of thevariance. The standard deviation of the list x1, x2, x3...xn is given by the formula:

sigma = sqrt(((x1-(avg(x)))^2 + (x1-(avg(x)))^2 + ... + (xn(avg(x)))^2)/n)

The formula is used when all of the values in the population are known. If the values x1...xn are a random samplechosen from the population, then the sample Standard Deviation is calculated with same formula, except that (n-1) isused as the denominator.

[dictionary.com].

["Barrons Dictionary of Mathematical Terms, second edition"].

Are you using a ball mandrel in your sizing die to get consistent neck tension?
Have you measured the neck O.D. for a sized and prepped case and compared it to that case when loaded?
Are you getting 0.001"-0.002" difference?

 

[Horns8491]

Some guys on here just lie about it. Have you tried that?

 

[lash]

Some guys on here just lie about it. Have you tried that?

???? Tried what????

Oh, wait a minute....you mean that some guys lie about getting single digit SDs? Why would they do that?

 

[Dave62677]

if you have time for weight all brass, turn the neck. Give it a try

 

[Steel head]

Some guys on here just lie about it. Have you tried that?

 

[Brux]

When I shoot a 5 shot group within that group they are running an average of 30 FPS difference.
Yes,I am using the die just as it came from the factory.
I have not measured the outside of the neck after sizing and after loaded.
I have weighed my cases and they seem to be weighing an overall difference of around 1 grain.

 

[lash]

Okay. So that is an Extreme Spread of 25-30 fps. That is not bad and if your groups are good and you are not shooting ELR distances like a mile and etc., do not worry about it at all.

With that ES, you may very well have a single digit SD.

To to sum it up. If your load is shooting well, say thank you and load up a couple hundred to get it going.

 

[supercorndogs]

^^^^^^^^^^^

 

[getoffmylawn]

For those of you that weigh brass, what tolerance do you allow for difference in weight when sorting?

Sent from my SM-G930V using Tapatalk

 

[TripleBull]

For those of you that weigh brass, what tolerance do you allow for difference in weight when sorting?

It depends in part on how many cases you have to work with, if they all are the same headstamp, etc. First, assume that problems like loose primer pockets or indications of impending brass failure have been dealt with and that those cases have been tossed. I don't like to mix brass from different makers, so I'll sort and decide which headstamp bin to work with. I mark new brass by lot and mostly work within a single lot if possible. Then I go weigh them and look at the distribution of the weights. You need to factor in how many firings the brass has had because if you full length size and trim a bunch of times, it's easy to measure the weight loss (and that also means that mass of brass has moved in those cases). Many people, after sorting down on all of the above, end up sorting into 3 weight bins. I'll also piddle around with a bit of case volume measurement, especially for newer brass that has a wide range of mass. Bottom line is that it depends and you don't need to toss the high and low weight bins as long as the cases have good integrity. Just load a bin together and at a later date work with the other bins separately. Many people have shot very well without weight sorting and many winning competitors do sort.