Newbie Load Development Question - How many rounds and how many grain increments?

Bart B

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Dec 25, 2005
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How credible is one group to represent real accuracy level?

Single group size times max/min multiplier equals approximate size limits of 19 out of 20 groups fired with different numbers of shots per group.

Shots/ Multipliers
Group Max ......Min
3 ..... 2.45 ..... .40
5 ..... 1.53 ..... .67
10 .... 1.27 ..... .81
20 .... 1.12 ..... .89
30 .... 1.09 ..... .92
50 .... 1.06 ..... .95

Examples:

If first 5-shot group is 1 inch extreme spread, 19 out of 20 will be from 1.53 inch to .67 inch.

If first 3-shot group is 1 inch extreme spread, 19 out of 20 will be from 2.45 inch to .40 inch.
 

Bart B

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I think Sierra's Mark Walker believes all 3-shot groups for a given load will be the same size.

Maybe he should tell that to the people testing their bullets during production runs and ask them to quit shooting several 10-shot groups. They don't work up a new load for different component lots nor a new test barrel.

His velocity numbers are not uniformly proportional to charge weight increments and that's not seen in vertical shot location. All bullets fired don't have the same BC so those leaving at the same speed won't have identical trajectories as proved in his 3-shot groups. I'd bet his ladder test would yield different results if repeated. Good tests of anything are so proved by repeating them getting the same results.
 

el matador

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For most of us it's not practical or wise to shoot 5- or 10-shot groups for load development. 3 shots is perfect. I use 3-shot groups to eliminate things that don't work and to narrow things down. Once I'm close on seating depth and powder charge I will do multiple 3-shot groups or 5-shot groups to verify.

If you shoot a 3 shot group measuring 2 moa, what is the probability that the same load will consistently be under 1/2 moa for the life of your barrel? Zero. That load is eliminated without wasting 2 or 7 additional shots.
 

TOM H

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I think Sierra's Mark Walker believes all 3-shot groups for a given load will be the same size.

Maybe he should tell that to the people testing their bullets during production runs and ask them to quit shooting several 10-shot groups. They don't work up a new load for different component lots nor a new test barrel.

His velocity numbers are not uniformly proportional to charge weight increments and that's not seen in vertical shot location. All bullets fired don't have the same BC so those leaving at the same speed won't have identical trajectories as proved in his 3-shot groups. I'd bet his ladder test would yield different results if repeated. Good tests of anything are so proved by repeating them getting the same results.

This is Mike Walker bio from Sierra

Mark Walker joined the Sierra Bullets team in June of 2000 as a design draftsman. Over the last 14 years, Mark has contributed to every product and project produced by Sierra Bullets. He is a ballistics professional, a skilled gunsmith, and an accomplished shooter. Mark’s understanding of the Sierra Bullets product line and usage uniquely qualifies him to help guide both engineering and production during the development of Sierra’s future requirements.

Mark commented, “My experiences drawing and designing Sierra Bullets production tooling, building the rifles for our test range, and competing in matches over the last fourteen years have given me a unique perspective on our product. I know exactly what we are currently capable of producing, how the rifle that will use our product is put together and why, and how our customers are using both to reach their goals in matches and in the field. I plan to apply all these lessons to help us produce exactly what our customers want and need.”

As product development manager, Mark will lead the development of innovative and unique new products that Sierra Bullets’ customers deserve.

Mark added, “While this job will bring many new and exciting challenges for improving all areas of our current product lines, I am extremely excited about using my position to help Sierra expand its offerings for the long range target market as well as make strides into the premium hunting bullet market.”

Mark is married with two children and enjoys 600-yard bench rest shooting, F-class shooting, and watching the Kansas City Royals in his spare time.
 

Bart B

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Impressive credentials.

But his ladder and group tests have low statistical confidence levels.

Even junk yard habitants shooting craps know they'll not get the same number between 2 and 12 on every roll. Group shooting bullets is akin to rolling several pairs of dice all at once.

Look up a benchrest match's several 5-shot group sizes then note their MOA's from smallest to largest. Quite a spread across a few dozen of them.
 

TOM H

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Impressive credentials.

But his ladder and group tests have low statistical confidence levels.

Even junk yard habitants shooting craps know they'll not get the same number between 2 and 12 on every roll. Group shooting bullets is akin to rolling several pairs of dice all at once.

Look up a benchrest match's several 5-shot group sizes then note their MOA's from smallest to largest. Quite a spread across a few dozen of them.



I would think before you criticize the article you would of contacted Mike Walker and see what he has to say.

As as me look up match results it would be nice if you posted yours so give posters here have chance to see what real BR shooter can do at a match. You might want to post your credentials that way everyone here could understand about Mike Walkers ladder/group test and maybe you have your article handy and post that so we can compare.
 

Jaxdialation

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How is it akin to rolling several dice specifically?

How many dice is "several"?

What is the confidence interval of his ladder test? His group test? Both together?

What is the confidence level of his approach?

During your design of load experiments, what confidence level and interval do you achieve?

Impressive credentials.

But his ladder and group tests have low statistical confidence levels.

Even junk yard habitants shooting craps know they'll not get the same number between 2 and 12 on every roll. Group shooting bullets is akin to rolling several pairs of dice all at once.

Look up a benchrest match's several 5-shot group sizes then note their MOA's from smallest to largest. Quite a spread across a few dozen of them.
 

TheLongRanger83702

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Feb 20, 2015
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Idaho
morning, i load 3 rounds. Check the barrel for heat, normally i load with .003 to .005

increments. if using unfired brass u could experience nominal group sizes. i have

found a good loading in first firing of the brass. the second firing of the brass

normally is where the groups start to get tight.

Alot depends on optics, customizing of weapon. shooting experience and reloading

experience and foremost patience.

bullet seat depth, brass prep, primers and make of bullets, and many more variables

that can a reloader pull hair out.

the people that run this site r extremely proficient and knowledge about reloading.

ask any questions, go to the search mode. do not b afraid to ask questions.

PATIENCE.
lightbulb I am relatively new to all this but have watched a lot of videos and read a lot of articles about what helps make an accurate rifle. I have bitten the bullet to NOT compromise on quality and create a "weak link" in my pursuit for accuracy. I don't know what powder you are using to accomplish .003-.005 grain increments. My scale is a $450.00 A & D EJ - 123 and can only weigh down to .020 gr. I use H4831sc and these kernels weigh @ .020 gr each. I use tweezers to get to that last .020 grain kernel in weighing my charges. So my loads can vary then by .020 at most. My velocities with this level of accuracy for powder charges varies on average @ 56 fps. I can't fathom getting powder charges any tighter than this. What scale and powder are you using?
Here's what I am shooting. For my testing I loaded 10% less than Nosler recommended for their 210 gr ABLR for my .300 Win Mag. I used Hornady 208 gr A-Max for my test bullet. My cases are Nosler because of their quality. From 500 cases, I measured 15 out of every 50/per box and ALL were below .005 run out. My primers are Winchester. I loaded 10 rounds each in .025 gr stages for a total of 200 rounds. I just randomly picked 65.75 gr string and shot these. Right off the bat I was at .25" group for a 5 quickly shot group. I repeated this after my barrel cooled. I guess I just got lucky right out of the gate. I stopped right there w/o going any further with my ladder test. Im pulling the bullets from the rounds I never fired and reloading them with the 65.75 charges. BTW, this is out of a new Krieger MTU 5R 28" suppressed & fluted barrel. My scope is the Nightforce 5X25x56 ATACR1 MOAR with their one piece scope base. My stock is an Eberlestock folder type for the Remington 700. I don't know if any single component or the combination of these components matters or not. Just mentioning them just in case. I couldn't be a happier guy after.

Later gun)
 

Bart B

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How is it akin to rolling several dice specifically?
Each pair of dice has the same odds of coming up with a given number between 2 and 12 for each roll. Each variable in the shooting system (rifle + ammo + human) has a few variables; the odds of any one being somewhere between zero and maximum closely equate to dice rolling numbers from 2 to 12 for most of the Gaussian probability curve. The rolled dice numbers are on a line at some clock face value with 7 at the middle representing zero, 2 at one end for a maximum minus deviation from near zero deviation and 12 at the other end representing a maximum positive deviation from zero.

23688520531_05496af37d_z.jpg


How many dice is "several"?
Several pairs are involved; each with different amounts of MOA values for each number of spots on the dies:

Pair 1 = Human holding the rifle; determines how far and what direction the bore axis at the muzzle moves from where it pointed when the firing pin strikes the primer. Each die number’s worth 1/10th MOA or more depending on how well the human consistently holds and fires the rifle from shot to shot. Variation axis is mostly horizontal but some will be vertical.

Pair 2 = Bore axis offset from center of mass that holds the barrel; includes stock, action and shooter. The more that axis is off the center of mass that holds it, the more it will change the bore axis before the bullet exits. The bore axis does not point to a place above the aiming point equal to bullet drop at range plus sight height above bore axis when the primer fires It points there only when the bullet exits the barrel.

Pair 3 = Cartridge case effect on where muzzle points upon bullet exit. If the case head is out of square with the case axis and not parallel with the bolt face, it will smack the bolt face at some point around its perimeter. That shock makes the barreled action whip on the axis that point is from chamber center. How much depends on the force imparted as well as if it’s in line with the bolt lugs. If 90 degrees from a 2-lug action lug center line, the whip amount will be the greatest. Die numbers are in 1/10th MOA increments. 3- and 4-lug actions reduce this problem.

Pair 4 = Bullet consistency in velocity, weight shape and balance upon exit from the barrel. If not perfectly balanced, they’ll jump off the muzzle axis upon exit in some direction due to centrifugal forces and have lower ballistic coefficients. Faster ones will drop less than slower ones. Effect increases with range. Unit value can be from 1/100th to 1/10th MOA for each number on the rolled dice. It’s mostly in the vertical plane. BC’s for a given bullet can vary 1% in good match bullets, more in hunting and arsenal bullets. Bullets not started straight into the bore will be distorted and unbalanced a little bit; they’ll take off in the same direction if their runout high point is consistent from shot to shot as it’s indexed in the chamber. Primer and powder has to perform the same for each shot so the pressure curve is the same from shot to shot. Weak firing pin springs and/or shallow dented primers cause greater muzzle velocity spreads.

Pair 5 = Atmospheric conditions. Winds blow the bullet mostly sideways. Thicker air density slows the bullet down and it drops more for a given range. Amount per unit varies but can be calculated with ballistic software.

Pair 6 = Barreled action unrestricted in its vibrations; barrel totally free floated. If not, then this pair of dice represents how much the barrels vibrations are altered by some pressure point on it or the receiver is not positioned exactly the same in the stock for each shot. Unit amount per number on the dice can be 1/100th to 1/10th MOA depending on the severity of the issue.

What is the confidence interval of his ladder test? His group test? Both together?

What is the confidence level of his approach?
With only one shot per load, I think all are about as close to zero as one can get. He could’ve verified how good of a ladder test he made had he shot one or two more the same way. If their results had a 10% spread across them, then I think it would have a very high probability of being a good test. I’ve yet to see anyone’s ladder test data from 3 identical sessions proving their worth having less than a 10% spread across them. One shot does not constitute a group.

During your design of load experiments, what confidence level and interval do you achieve?
I think a 95% confidence level is attained when I shoot 20 shot test groups with a given load that 19 out of 20 such groups will be no more than 12% larger to 11% smaller.

A 3-shot perfect triangle group at 100 yards with .5 MOA between shot holes has a real accuracy level somewhere in the range from approximately .2 MOA to .8 MOA according to:

Closed Form Precision - ShotStat

I've never worked up any load for .308 Win or a couple of 30 caliber magnums for different bullet weights save for one new bullet for which no load data had ever been developed outside of Sierra Bullets test range. Just used the same ones the match winners and record setters used. Shot test groups as small as any across several barrels.

Having oft times seen benchrest match results for the top 10% in aggregate group average sizes over the years, it's easy for me to see that their 5- and 10-shot group sizes fired at all ranges have the largest groups several times bigger than the smallest ones. And rarely is the smallest one in a given match the first group shot. Go to:

http://benchrest.com/showthread.php?93618-2015-NBRSA-Nationals-Complete-Results

. . .then open each file and check all the group sizes for the top 10% in each match. Do your own grade school math to see the range of sizes they are.

A favorite "statistical improbability" is the record 100-yard 5-shot group of .0077" held by someone who holds no other records
 
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