OzFclass

es & sd is a most interesting topic.
while I am probably not correct here, I believe that s.d. is the critical number, and can only have meaning for 10 or more shots. the more shots, the more meaning.
the true e.s. for a 10 shot sample is somewhere in the region of 4 x the s.d, while the e.s for a 20 shot sample is 3 tines the s.d.
this suggests that the e.s. for that sample is less than for that load, and this is where e.s. aficionados get surprises.
it has always been said that an s.d of less than 10 is the goal for long range shooting, but the tighter fclass target might demand smaller s.d.
however, an s.d. of 7, even for 20 shots , is probably the same as an s.d of 10 id terms of e.s., and getting lower numbers is not easy.
why this is I do not know. black powder can be made to produce s.d of 4 quite easily. is this to do with ignition &/or burning of powder?
all this said, it is the paper that must do the talking.
in the end, while a chronograph is a helpful tool and can speed things up, it is not absolutely necessary.
here in s.a. testing ammo at 1000 can often be difficult, due to range availability, and weather. oh for a range like dave's.

Paul,
I did say easy to push in, But really what it is, all projectiles "feel" the same going in and not difficult, although not seated that far in, maybe not quite half way down the neck, then the boat tail sits about where the shoulder starts. I thought about the right seating position? this gives me .010" jam. definately not loose.
looking at my Chronograph info last night, my SD is nearly half of the ES reading so it maybe a projectile thing or technique.
So, the SD is quite good (5) but doesn't shoot all that well so it may well be something else if SD is more important than ES.
Geoff

You can still get acceptable SD readings even with an ES of say 40 f/s
For example--
A 10 shot string gives an ES of 40 f/s but 9 of those shots only go 12 f/s.
It's the 40 f/s one that costs you and most likely you adopt the attitude of "oh well probably helped that one out "
This situation is common place and highlights the fact that 3 or 5 shots do not prove much.
On the other hand if the rifle is at best tune point that 40 F/s one could just be in.
Others will bear me out on this one -- I have seen low ES ( under 15 F/S ) shoot lousy groups while large ES ( unacceptable ) shoot tiny groups.
Low ES alone does not guarantee accuracy.

Ive raised the question on accurateshooter. And it looks like my thoughts that ES is the critical number is incorrect. Im no statistician but I still would have thought the SD would be relative to the ES. German Salazaar gave an example of 14 or so shots all at 2850fps then one at 2900fps. He said then that the SD is still good, but the ES isnt all that good. Personally, if i had 14 shots at 2850 then one at 2900 I wouldnt believe that one shot was prepared the same as the others.

Happy to stand corrected. There is alot of debate on the two forms of statistics on the web. But like everyone has said end of the day its what it does on target that is the key.

Geoff, you said you load your rounds to get to a certain velocity, then work in that area. Would you not start low and work up to what is accurate? I know we need to maintain velocity to get to 1000yds but if you have a slow barrel and your pushing pressure to get your rounds to stay supersonic maybe there is some inconsistencies starting to develop? I know velocities are important but end of the day consistent accuracy is our game. Also what chrony are you using? It seems the magnetospeed is the one that most are using now for reliable results. If its one that relies on light, there can often be some error in the readings. I dont know if I would trust a light sensing chrony unless its one of the big dollar ones. Definitely my F1 is very inconsistent, where a mates magnetospeed makes me look like a reloading genius

The odd shot within a string that gives Speed far removed from the average is generally not due to bad loading. You will never know the reason as that shot cannot be fired again. However, you can determine if the case is the problem by repeated loadings and firings. If it gives consistently odd readings throw it away, if not then the initial problem was with the projectile or primer ( assuming powder load was good )
I agree with Brad - Sometimes trying to achieve 1000yard accuracy in a particular barrel with a particular combination of components simply does not work. You have to change.

So much to say here....sorry everyone and no real time but may come back to this after Raton.

Understanding "populations" is the key to this. We have a "population" of shots that represent every shot we will ever fire with this load. When we test it we only take a small sample of this. The sample doesn't necessarily give you a good representation of what is going on in the whole population and can by luck lie anywhere within your whole population. A small chance you will see the edges and a much greater chance the sample will lie near the middle

A "normal" distribution basically means you can expect 68% of your shots
within +/- 1 standard deviation of the average, 95 % within +/- 2 SD and 99+% within 3 sd's. Here is a graph. http://upload.wikimedia.org/wikipedia/c ... iagram.svg

Firstly a lot of chrony's can give aberrations (false readings) that can lie well out of the standard population. So can a faulty bullet, bad primer etc. Effects can be imaginary (ie just the reading not the actual velocity) or real (e.g. human error and powder charge several grains below targeted amount) that can cause extreme outliers. From all that I have seen in shooting the general population (for want of a better term) of shots follows a "normal" distribution in most situations but the outliers can be way outside "expected" values (>3 sd's away).

Please take the time to understand this and note "errors" can lie outside this and can be discarded when assessing loads but if it is a regular occurrence then you should look into the reason and fix and control (quality assurance??)

When we "sample" our population (ie do a test of some sort and take the readings). Luck and coincidence can mean the data can come from anywhere in this group but with small samples there is a great chance that you will sample from the middle and not see the true variation of your "population" We can get false positive readings in our sample even though the whole population might not look the same.

Therefore es of small samples means didly squat but similarly sd of samples less than 10. If you are a benchrest shooter and measuring total group size then there is an argument for using ES (as your group size is determined by the outlier) but as score shooters we should only be interested in the sd but understanding what it means is the key.

Herein lies the conundrum. We don't want to shootout our barrels in testing so we tend to use small group numbers. I showed a technique earlier in another thread which can help "cheat" with the stats or add power to small samples if done in a ladder but really what most shooters do is use small groups to try and quickly find "areas of interest".

Back to Geoff - sd of 5 shot groups is still misrepresenting the total population and will be lower than the true sd as Bruce indicated but it certainly sounds like you may have an issue outside the loading.

thanks Dave for your professional input. I'm now thinking of other issues that may more of an influence.
Brad Y,
Yep did start low (2700f/s) and worked up. 2960f/s was the best ES & SD although I thought ES a bit high.
When I went up to & over 3000f/s which is where i wanted to be, ES & SD went higher. As high as 60. couldn't go higher due to pressure issues.
So, other issues I think. Plus I'm probably trying for the impossible.
I'm using a Magnetospeed, so assuming it's correct. And it's way better to use and store data
Geoff

Care to share caliber, load, rifle details etc?

Krakey
I have never seen a chrony win a shooting competition
Use as a guide only the group on target tells the truth (somewhat)
Don’t chase velocity chase consistent accuracy sometimes this coincides with desired velocity and most times it doesn’t
I did have a chambering that wasn’t right and would through 1 or 2 shots low at 4 O’clock mid string on a regular basis rechambering fixed the problem.
Chrony’s aren’t NASA certified and usually have a + or - 1% accuracy
What’s 1% of 3000fps?
RB

RAVEN wrote:Krakey
Chrony’s aren’t NASA certified and usually have a + or - 1% accuracy
What’s 1% of 3000fps?
RB

Richard, I'll help you out with the math! The answer to whats 1% of 3000fps is 30fps. Its not NASA who do the certification its NATA but close enough I spose to make the point that there is indeed accuracy errors in all instrumentation. Some instruments have much smaller errors than others and this fact is why the electromagnetic sensors on the MagnetoSpeed make it a standout chronograph.

In the link below you will see that the test conducted on the MagnetoSpeed when tested with a double Oehler system returned a 99.6% level of accuracy and when tested to a higher level with high speed video it returned a 99.9% accuracy level. Thats a pretty impressive level of accuracy and 0.1% (99.9%) of 3000fps is of course 3fps. If we look at 0.4% (99.6%) error we get a resulting 12fps.

The MagnetoSpeed Chronograph is accurate and relatively inexpensive and makes a great load development tool!

http://www.magnetospeed.com/pages/reviews-tests

Ian

Ok, Brad y,
I can hear the groans coming,
Info; 6XC using 2213sc powder, Barnard action on Vee block. 1:8 twist barrel, Norma XC brass, Dtac 115gns -ex Tubb, Barrel now 300 rounds.

It has shot a couple of good scores, but, not where it should be according to our American friends using the same ingredients. The best, score -wise was @ 2960f/s it should be over 3000f/s with the case size.
I have used 2209 for some testing but it didn't really fill the case as i thought it should, groups were big.
So maybe my chasing lower ES to get smaller groups may never happen due to other other influences ie, incompatible barrel, calibre, powder projectile etc etc.
Geoff

Righto, Im not familiar with the cartridge, but I have heard from a few people that the 115gr 6mm bullets can be pains in the butt to tune. Plus berger recommend 1:7 for theirs and I dont know what stabilisation would be like with the DTAC in a 1:8. Remember alot of US shooters are shooting at higher altitude than us and can sometimes get away with twist rates that we cant.

When I started working loads for my 6.5mm (will do for the new rifles I have coming as well) I started with one bullet and one powder. If I was getting inconsistant results I would first change powder then the bullet if there was no joy. Lucky for me that didnt happen. But if your not getting results you want mate, I would go looking for another bullet. Just because you are shooting the same calibre and twist and load someone in the USA does, doesnt mean your barrel will necessarily like it too. You have tested powder already so I would change projectile. The 105gr hybrid has a very good BC and the 103 copperhead is rated highly for long range too. The extra speed you drive them at will make up for any (if at all) lower BC than the DTAC. Both stabilise fine in an 8 twist.

Barrel life is too short to try and make something work if it refuses to do so.

Good luck with it.

Krakey wrote:Ok, Brad y,
I can hear the groans coming,
Info; 6XC using 2213sc powder, Barnard action on Vee block. 1:8 twist barrel, Norma XC brass, Dtac 115gns -ex Tubb, Barrel now 300 rounds.

It has shot a couple of good scores, but, not where it should be according to our American friends using the same ingredients. The best, score -wise was @ 2960f/s it should be over 3000f/s with the case size.
I have used 2209 for some testing but it didn't really fill the case as i thought it should, groups were big.
So maybe my chasing lower ES to get smaller groups may never happen due to other other influences ie, incompatible barrel, calibre, powder projectile etc etc.
Geoff

Geoff, Brad got 2 really good links from his thread on accurateshooter.com have a read of this one and you may just give away chasing ES http://riflemansjournal.blogspot.co.uk/ ... oters.html

The velocity you are getting is dependent on your barrel and chamber just as much as case and bullet. Sometimes the combo you are using will not get the velocity claimed by other shooters. Brad's advice of trying another bullet sounds good to me!

This is the other link that Brad got posted on interpreting groups. Its worth a read. http://www.the-long-family.com/group_size_analysis.htm

Ian

Krakey
Find out were your info comes
At what elevation ASL was the testing done
The issue I had with vertical was a 6X47 very close to the 6XC in capacity out of 1:8 twist button barrel.
I now use 1:7.75 & 1:7.5 twist cut rifle barrels for the 115 Berger and DTAC
Very nice to shoot!

Thanx for the math Ian where would we be with out you!
The magneto speed is certainly impressive and the degree of accuracy would be increase with fewer environment issues between the muzzle and screens.