What are the SDs of the velocity spreads for your long range ammo reloads?

Please be honest!

Also, what are the most important reloading techniques - in your opinion - for reloading the most consistent velocity ammo?

If I understand your question correctly, when competing in Long Range matches, 1000yd. and Palma matches, made every effort for the loads to have no more than single digit variation and at times the chronograph would show numbers as low as two to three fps, in short almost same for as many as 8-10 shots, best I could do with my reloads for the particular rifle and 308.

quote:

Originally posted by Instructor:
If I understand your question correctly, when competing in Long Range matches, 1000yd. and Palma matches, made every effort for the loads to have no more than single digit variation and at times the chronograph would show numbers as low as two to three fps, in short almost same for as many as 8-10 shots, best I could do with my reloads for the particular rifle and 308.

Thanks for the feedback.

What were the import reloading techniques that produced your velocity consistency?

AIU;

What ever you do process wise- do it exactly the same for very case in prep, every powder measurement and every seating step.....

The steps I took to produce the best loads I could included thorough cleaning of brass, cutting/reaming primer pockets to remove residue, trimmed the Lapua brass , carefully weighed powder charge via electronic scale/thrower, seated bullets some .003" off lands and grooves, weighed and sorted both brass and bullets for consistency for each load and after loading a batch of 100(days worth of shooting w/ extras,) weighed each complete round and checked run out on dial indicator for concentricity check.
When finding rounds not to my liking would sort those out for practice/range use but that usually only mean half a dozen or so rounds. Used all manner of brass but much preferred the Lapua brand over the others. Some of those brass had been shot at least 8-10 times and only when the neck would split would discard them. Might mention that technique I used for seating bullets that gave me the run out I was looking for was to rotate the brass two to three times as I seated the bullet to the desired depth. Did it help, seemed to do so for me. The one step I did not do is to turn necks as many do in precision shooting, but just did not want to take the time to do so but did make High Master Long Range using the above steps(only took me some 40yrs. of shooting.) Due to age and corresponding health reasons no longer compete, but recently did complete build of Rem.700 action/Douglas 12 twist/4groove barrel, solid walnut Rangemaster style stock,bedded, 308 and using some of the old reloads as described above the rifle is very much a sub MOA rifle with Leupold MK4 M1 10x scope at ranges out to the 600yd. line(these days off the bench of course.) With the 308 at ranges of 600 and beyond it is important that you eliminate as many variables as possible for each and every round because me the trigger puller in prone with sling and micrometer sights is more than enough variables to handle.
Those were the good old days, but I remember them fondly.

Thanks for the detail - I appreciate it.

Did anyone try anealing the cases?

If so, how often?

I anneal after every firing for my long range rifles.

Variable neck tension is an accuracy killer.

A good concentricity gauge is also a great help, as is testing to find the best CBTO*.

Rich

CBTO = Cartridge Base to Ogive. The amount of distance a bullet moves before the ogive hits the origin of rifling might be the most critical.

From my review of causes of velocity variation (high stand deviations), to get the most uniform velocities and keep your SDs at near 10 or less, one needs to...(the below assumes you have a action that has been trued and squared up, such that the action is not causing vibration and concentricity problems).

1. Minimize variance in "shot-start-initiation pressures (SSIP)". SSIP is the pressure needed to overcome bullet pull-out resistance and rifling engraving resistance.

2. A variance of only 1000# PSI in SSIP can result in a as much as 20 fps difference in muzzle velocity. (See QL and play with the effects of variable "shot-start-initiation pressures" and its eventual effect on overall PSI and muzzle velocity. It's striking.)

3. To minimize variance in SSIP, one needs to have uniform neck-bullet tension and uniform bulet jump distance to the lands. Having near identical CBTOs minimizes variance in bullet jump. Seating the bullet into the lands causes a marked increase in SSIP (indeed, QL says an increase of 7200 PSI).

4. Neck-turning uniforms case neck thickness and significantly helps uniform neck tension load-to-load. Some advocate annealing cases after every firing, but others say that is unnecessary. I've been able get SDs below 10 without annealing. The neck should be resized with a BR neck die with a "proper" bushing and only tight enough to just "hold" the bullet.

5. Cleaning the neck also helps uniform SSIP. (Also, I’m experimenting with creating a thin film of graphite on the inside of the neck, just before adding powder and before seating the bullet. (The graphite lubricant, during bullet seating, also acts as a lubricant to help concentricity.)

6. High concentricity (minimal run-out), also insures that the bullet hits the lands straight and not at an angle. A bullet hitting the lands at an angle can cause a momentary "obstruction" (thus increasing SSIP) and abnormal vibration (with the latter adversely effecting accuracy as well). If concentricity is highly variable, it is clear how one would have variable SSIPs. Neck-turning helps concentricity.

7. Weigh powder charges very accurately, at least to the tenth of a grain, some say to a hundredth of a grain.

8. Use match primers with uniform brisance. (I’m using CCI BR primers.) Also, uniform/clean primer pockets and holes with deburring, if needed. Some advocate using relatively "cool" primers to uniform ignition, such as large-rifle primers in magnums.

9. Use cases with uniform volumes. Some advocate checking bullets for uniform bearing surface, bullet to bullet.

FINALLY, DO ALL OF THIS CONSISTENTLY, SUCH THAT EVERY ROUND IS ESSENTIALLY IDENTICAL TO ALL THE OTHERS!!

about three of those relate primarily to uniform neck tension.

For most cartridges, Lapua is the best bet to get uniform brass.

It is good enough (within 2gr on my 6.5-284 brass, and .0015" oal) that it does not benefit like American brands do from culling. The flash holes are drilled, and the primer pockets are cut, so the depth varies less than .001". Wall thickness varied by about .001" as well.

Example: I wanted a Case-Gard 100 full of them. I just called Bruno's and ordered 120. There was no bell curve, so I just took the 20 heaviest and will use them for load work.

I also use a sonic cleaner, so no crud to contend with.

There are a couple things to deal with with American brass, like when I built my 22-284. I bought 500 Winchester 6.5-284 cases, and culled until I had 200 good ones.

A shooting buddy was a bit critical of my methodology and the extra cost, until I asked him how much we spent for a tank of Diesel for my Dodge or his Ford.

IS,

What SDs are you getting?

AIU

If I recall correctly the standard deviation is the square root of the variance divided by the sample size, or something close to it.

So what are you asking for. Are you defining for the whole population or for each sample (say each time a person goes out and shoots) or for some other specific sample size.

7-9.

I still struggle at times with the importance of the low SD as it is discussed by Brian Litz in his books.

His assumption that the SD will be greater the more shots are fired is at odds with my results with accurate rifles. If the first ten shot group at 100 yds is under 1/2", why would ten more groups increase the average size.

I had a very accurate HBR rifle in 308 Winchester. A tight neck. In four years, and over 2500 rounds fired in competition, I never shot a score under 245 at 100. According to Litz, at certain intervals every group should have been bigger (lower score).

Same with the 6PPC Fred Sinclair built for me. At about 1800 rounds the rifle stopped shooting in short order. Worn out barrel, not statistics.

quote:

Originally posted by Idaho Sharpshooter:
7-9.

I still struggle at times with the importance of the low SD as it is discussed by Brian Litz in his books.

His assumption that the SD will be greater the more shots are fired is at odds with my results with accurate rifles. If the first ten shot group at 100 yds is under 1/2", why would ten more groups increase the average size.

I had a very accurate HBR rifle in 308 Winchester. A tight neck. In four years, and over 2500 rounds fired in competition, I never shot a score under 245 at 100. According to Litz, at certain intervals every group should have been bigger (lower score).

Same with the 6PPC Fred Sinclair built for me. At about 1800 rounds the rifle stopped shooting in short order. Worn out barrel, not statistics.

It is obvious you never studied statistics or engineering ISS. Litz is right. I am in Mexico and don't have his book handy, but I think his point is that the more shots you fire, the bigger the group, no matter how accurate the rifle. At some point you will approach the absolute group limit, but firing additional shots will not make the group shrink - it can only increase.

Litz has some great stuff on long range shooting - specifically that you can mathematically model the odds of hitting a certain size target given wind estimation errors, rifle accuracy, etc. But to some on AR, there is no limit to what one can do with a rifle and those who can't are just jealous or some other inane non-scientific explanation.

your comprehension level has slipped another notch. Add something that you have empirical data to support your statement. Otherwise you are just a jackass braying to hear himself.

SD assumes the more rounds you fire, the larger your groups will be. To back this theory up the theory also assumes the more rounds you fire, that your MV/SD will double, and then triple.

My contention is; if you have produced quality ammunition, the first and last targets you fire will vary less than 10% in group size. Groups do not go from 1 SD to 2 SD's to 3 SD's as the number of shots fired increases.

I am asking someone here with an IQ over 100, not someone in the low-80's like you to share knowledge.

I have Berger's Manual, and all of Brian's books. I have read them all, more than once. I spoke with one of Berger's Techs this morning about a simple working definition of SD. He tells me that SD is so complicated, that it takes a computer and pages of simulated and/or actual round count to figure it properly. In other words, it cannot easily be explained.

ES (extreme spread) is simple. The difference in fps between your slowest and highest MV.

AV (average velocity) is simple, it is the average MV of the number of shots fired.

So, based on your blathering, it does not appear that you have a clue as to what is either. The difference, is that I can admit it, and that you're incapable of explaining it or admitting your ignorance.

In plain english, it means you don't have a clue either.

To quote Brian Litz: SD is a better way to characterize variations in MV related group sizes (than ES or the actual sample group fired). He backs up this assumption as "One powerful way to use SD is through confidence intervals.

Who determines these "confidence intervals"?

SD can be used to make predictions about your data, and to assign a confidence to the prediction. Specifically, you can say that:"
68% of the shots should be within +/- 1SD of the average
95% of the shots should be within +/-2 SD's of the average
99.7% of the shots should be within +/-3 SD's of the average.

That means that 68% of your shots will be within +/- 1 SD, which, if you have an SD of 10fps grows your ES to 20fps.
That means that 95% of your shots will be within +/-2 SD's which, if you have an SD of 10fps grows your ES to 40fps.
That means that 99.7% of your shots will be within +/- 3 SD's, which means if you have an SD of 10fps your ES will grow to 80fps.

If that is valid, no wonder the group size gets larger, you are shooting crap ammunition or you are a really lousy shooter.

The closest he comes is in the glossary of Berger's book.

Standard Deviation: a statistical measure of variation within a group of data. Typically used to describe the variation in MV or the spread of shots in a group.

Drawings in the Berger Manual or all of Brian's books, tend to show computer generated plots of multiple groups (up 1000 simulated shots) to support the SD value.

In other words, the SD gives you a likelihood of how your data (velocity in this case) will be distributed around the average. He uses a bell curve to illustrate his theory.

Where I question this, is why the more shots you fire, SD says the larger your group sample size (cumulatively) will grow, and the higher your SD's will be.

I know somebody out there can explain this in real world terms.

Knowledge is what I seek, and enlightment...

Rich

Another question worth asking; is 2-3 FPS within the measurement margin of error of your chronograph?

P.S. My, how quickly we degrade from thoughtful explanations to puffing up and hurling insults...