I'm fairly new at reloading and maybe this has happened to other's as well, during load development I will load 6 of each powder charge and combo and go out back and shoot for an evening. After the shooting session I will pick which load shot the best, go back inside and load 15 or 20 so I have them. The next time I shoot them, they may not shoot the same (point of impact or even hold the same tight group) then I'll go out and shoot one of the other loads I chose not to load a bunch of because they didnt hold the group the others did, and they will shoot as tight or tighter than the one I chose. In short, I was shooting 2 or 3 groups of 3 and deciding on a "sweet spot" load, is this too quick to determine? As the thread title states, how many shots until you can trust a load to be what you want it to be?

Your experience is not uncommon.

I find it useful to graph group size vs powder charge. This shows trends over a range of charges, and tends to average out peaks and valleys of individual groups.

I'll load 5-round sets over a wide powder-charge range, and pick out a narrower range where accuracy seemed better. Then, I'll load some sets over the charge range that seemed best, in smaller increments.

This serves to hone in on the ultimate charge, and duplicates the experiment to avoid the spurious results you're seeing.

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Change in temperature changes barrel time and can move a sweet spot. Ideally you want a load that is accurate over a fairly wide charge range, then load in the middle of that range. That way a temperature change tends to move the right charge within the range. You might want to take a look at Dan Newberry's Optimal Charge Weight load concept and his round robin method of evaluating loads on his pages here.

To answer you question more directly, there are a couple of rules of thumb used by statisticians. One is that it takes about 30 samples of random data to get a bell curve that isn't slanted and thus your confidence can be reasonable. My old company's statistician liked to say that nothing of significant confidence can be done with less than 21 samples, and that was for really minimal confidence. 30 or more was much better. He also said you should estimate how many of something you would make, then use a sample size of the square root of that number plus one. So, if you figured your barrel had a peak accuracy life of 3000 rounds, and you were going to use the same round throughout its life, you would want the square root of 3000 + 1, or, rounding up, 56 rounds. If you are going to shoot 1000 rounds, then 33 sample rounds should be fired. The bigger the sample, the greater the confidence that you won't see a round that performs outside the extreme spread of your tests, and that the standard deviation is correct.

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Okay, credentials 13yrs of competition bench rest. Use the highest power scope available. Many should buy a cheap Tasco 8-32 with 1/8th minute dot just for load testing. Works well when you are shooting at a notebook reinforcement with a hole that is 1/4 inch in dia for a target pasted to an old grocery bag (same color as a deer) if your sure you are on target it takes a lot of guesswork out of load developement. Don't shoot for speed, a chrony is for speed consistancy. Shoot for groups you owe that to your quarry.

Deer rifles, 3 rd groups

Varmit rifles, 4 rd groups no more than five

Heavy target rifles, whatever competition you are in.

Some very simple things to do, bring a .22 with you and a couple of other guns. Shoot each to foul the bbl, leave gun with bolt open to allow cooling. Deer rifles I shoot three round groups and allow 5 minutes between shots.

Varmit rifle, 4-5 rd groups with at least 3 minutes between each shot, after all if you are prarie dog hunting shots may come less than a minute apart.

Heavy target, again if you are into this you will know what to do.

Above all use your head and feel the bbl every so often, when you can feel the heat it is time to shoot that .22 some more.

The number of shots per group doesn't mean squat unless;

1. The ammo is uniform and precise. That means uniform in bullet weight, case weight, powder weight, COAL, within pressure parameters and barrel twist weight for bullet length.

2. The shooter is using some kind of gun support, to eliminate as far as possible, shooter error.

3. Use of some kind of chronograph to determine average velocity and overall standard deviation.

4. Some kind of notation system to keep the information in a relative cogent form.

5. Some kind of common sense level of accuracy for the weapons capability and/or it's intended use...i.e., competition, varmint hunting, large game hunting, target, or defense. Spray and pray isn't anymore effective for varmint hunting than it is for defence use.

The above are minimum requirements to begin a "scientifically accurate" basis of recording your data.

I've always used 3 rounds to start to see if the load will group and to not waste time and components, then 4 shots if the group shows promise, then 7 shots. You can play with statistics or pick 5 and 10 shots as a basis, but if a load will put 7 in a small group, why waste more on paper...I would rather be shooting squirrels or something to eat than paper.

Pick a bullet, powder and primer, use reloading manual published loads starting in the middle of the powder range. Shoot two or three groups. If the load looks promising I start working up slowly. Normally, loads near the top of the range are the most accurate...the groups will start to get smaller as you go up with the powder amount. Someplace along the road the groups will open up. That is the place to stop and drop back to the precious most accurate load. This way has always worked well for me but is not cut in stone. The best way to learn is to read all you can and shot a lot.

6mmBR is one of the best forums for learning how to shoot and reload and there are several very good articles that will explain this process much better than I can or have the time to try to squeeze 50 years of shooting into a few words. Precision Rifle is another. Both sites and the information presented mostly leave out the ego and pecker waving and are based on sound practices. There are a bunch of long range and varminting shooting forums that are excellent also, but you have to do some digging on the web and on forums yourself.

http://www.6mmbr.com/index.html.

http://www.freewebs.com/precisionrif...cyarticles.htm

Goto Accurate Reloading and check out the data for all the weapons. It is full of great information if you read with an open mind. It illustrates most eloquently what powder weight changes can do to accuracy...it doesn't matter if it is a weapon for varminting, wasting large ego enhancing beasties or just protecting your azz.

http://www.accuratereloading.com/index.html

Be carefull of what you read on forums as we men have egos that need boosting continually and tend to play fast and loose with what we consider "truth", and we all have different ideas about what "accurate loads" means. You know the old saying "one mans garbage is another mans gold", and people still get shot over which auto/truck/MC/caliber/etc is better. You get the idea. There are many more knowledgeable people who DON'T post on the net than those with large egos (like me) who like to make noise and strut around playing tom turkey.
It takes time to learn this sport and the road is windy and takes off in strange directions all along the way.

'Njoy

i agree with NFG as far as sentances # 1 and 3.
consistant cartridges (seating depth, case prep, bullet runout, charge weight, etc) and the use of a chronograph are critical or you're wasting your time.

I don't think it's that absolute. Bootz Obermeyer pointed out that some load and gun combinations seem to be more immune to shooter position that others, independently of how they grouped on the bench. This is a test most shooters fail to make if they are planning to take the gun out into the field or to a position match. By definition, this can't be tested on the bench, so the only option is putting groups on targets from actual shooting positions that will be used. When you introduce the noise of a shaky shooting position, you need more than three rounds to reliably find a statistical center and standard deviation of group size.

Since competition targets are commonly shot in strings of 10, I've always assumed groups of three came about because hunters wanted to test that a cold shot and two fast follow-ups would stay within minute of game. Presumably, the hunter would cool the gun and, if he expected to carry it unfouled, clean it, then repeat the exercise until he accumulated enough of these groups so performance was likely to be proved. Statistically, three shots in isolation are meaningless. They have value only when they are part of a larger pattern, such as a round robin, or, simply as an extension of a past history of grouping capability with the gun. In isolation, even three shots through the same hole, despite the improbability of that being entirely coincidental, doesn't offer confidence that it is representative of the gun's behavior.

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I've often wondered how many serious handloaders were engineers.

I do a bit of work in the area of design space optimization and statistical process controls. I think your aprroach is a good one, and six shots is probably sufficient to identify a trend, getting better - getting worse.

The thing to decide is which factor you will evaluate in a series.

Typically I'll consider a load for some application, pick one out of a couple of references, hopefully one that nosler or Lyman found as "most accurate in the weight/type of bullet, and determine the max for that load from the reference.

My next step is to load 4 sets of three shots each, each group 0.5-2gr more at each interval with the max load as the top end ofthe list. For a 45gr max load of X powder in a .243, I would load 42gr, 43gr, 44gr, 45gr.

I then shoot each group of three to see if there's a trend from top to bottom. Do the groups shrink or get larger over the series? Then I narrow the range and load up sets of 6. My own qualifier is whether I can shoot 4 consistant groups on one target.

TMan,

Check Dan Newberry's system out. I think you'll like his 3-shot-per-target round robin approach. It seems to be an excellent evaluator.

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"First contemplation of the problems of Interior Ballistics gives the impression that they should yield rather easily to relatively simple methods of analysis. Further study shows the subject to be of almost unbelievable complexity." Homer Powley

Thanks a million fellows, the info brought here has my head spinning, but it all makes sense. I never knew the loading gammet went so deep when I got into it. I will continue the research on the web links provided and keep on keeping on. I'm not miles away here, my groups are generally decent and hold true, but I did want to explain what happens from time to time and I was just curious if I was alone in this. If anyone has anything els on this I will absorb it like a dry sponge.

Smitty - all good points above.

If you do an Archives search (bottom of page, click on the Archives icon) for
"Benchrest Techniques", you may get a little additional help. They way you hold and place the rifle on the rests on the bench will cause significant group wanderings.

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i like the "sweet spot" theory to find my starting spot
then i try to fine tune that load i.e. primers and seating depths etc
this is done with the same target with a new one over it for each new test.
then when i am happy with it [ chambers smoothly is consistent for temp]
then i will usually shoot one 50 round group over a short period of time usually in the spring
as this gives me a variable of temps and conditions.
by now i either really like the rifle or am looking for another.
but i usually know whats up with this rifle within 100-150 rounds

See how quickly all the good stuff comes out!!! There are lots of "methods" for testing, but all have basics in common...a starting point, determination and elimination of "bad" effects...effects being those bits and pieces the cause erratic patters. Lots of measurments of ALL the parameters..i.e., bullet/case/primer/powder weights...bullet uniformity...i.e., bullet ogive and OAL, weight, runout, internal voids throughthe use of specialized equipment.

Many times I've worked up a load that seems to shoot very well only to have it go to H*** in a breadbasket. I uniform the brass for every weapon I have, be it pistol, shotgun or rifle. Start with at least 100 cases, weigh sort first to eliminate the outliers...those that fall outside an average weight that I determine after all are weighed. The primer pockets get cut to uniform depth and the flash holes get deburred, the necks are measured, an average taken and then turned enough usually to about 75 to 80% of the average runout. As this process continues any case that falls outside the statistical mean gets tossed into the "use for fouling" pot. If I end up with 50 out of the 100 all as uniform as possible within a "range" then I'm happy...unless the cases are Lapua or Norma...then I better end up with 85 to 90%.

Out of the keeper group I pick 10 to use for load testing. On many occasions I have loaded and fired a 5 round group in the 2's or less, go back and reload the same cases with the same powder/primer combo and fire it within less than 15 minutes and have the group open to a 5 or more. Same 5 cases, powder, bullet brand, primer, COAL, exactly as close as I could get them to the first 5 rounds. The only difference that I could determine after scratching my head for a while was a difference in the Ogive contact point and bullet end point. Many times I found a different ogive point in the bullets in a box. I've found 3 different ogive points in boxes of Hornady bullet...not once but several times. I've also found the same thing happen to every brand of bullet I've ever used ot a greater or lesser extent.

That difference doesn't cause problems in bullets for hunting or if your level of accuracy is in the 1"-2" range but if you're shooting at a 1.5" x 4" potgut at 400 yards or trying to win a match it can make a the difference between winning and ending up last or having bragging rights to the longest shot of the day.

I measure every bullet in every box I buy, establish "statistical" mean, roughly and keep those that fall outside the range for fouling shots. I don't get anal about it anymore as I don't compete with anyone but myself and I'm getting a bit lazy nowdays, and it doesn't take long using a set of Stoney tools. I've run tests on all my guns with the bullets I prefer and I check the throats fairly often. I adjust the seating after about 500 rounds depending on the caliber or when the accuracy starts falling off.

There a thousand and one things that can be done to improve accuracy or make your shooter perform better and at least a million ways to do each and every one of them. How much you do depends on another thousand or so reasons. Just enjoy what you do and don't get your shorts all bunched up...it takes all the fun out of sitting down and shooting.

There are lots of tools and electrical devices available to the drudgery out of uniforming cases, keep check on throat erosion, measure and prep bullets and cases, weigh powder. Lots of information available on what to do to make your shooter more accurate, and lots of ways to get there. Take your time and enjoy.

'Njoy

Smitty - don't underestimate the importance of shooting technique and supporting the gun in the exact same manner during load development. I have a Ruger #1V 25-06 that was giving me fits during load development. One of the forum members, I think kdub, offered a #1 could be a little finicky if not supported in the same manner during load development. I recall the suggestion was to support the gun near the action and do it the same all the time. Bingo.....I started getting very repeatable results and load development went a lot smoother. I don't shoot competition, handloading/shooting is my hobby, and I don't have a fancy adjustable rest, I use an Uncle Bud's Bulls Bag or a similar rest at the range. But, I do make it a point to eliminate as many variables as possible and being consistent with shooting technique is one thing I can control during load development. What worked well for my #1V works well for other guns too. I do a ladder test (like Nick is suggesting) to zero in on a load range and tweak it from there. The ladder test works when done properly.

My 5 centerfire rifles are all factory guns and with the exception of replacing the flimsy synthetic stock on my Fireball with a laminate stock, they are all original. I handload for all of them and am very pleased with the accuracy I get from them with my handloads. I think you get the idea you should try different things but don't try them all at once. Part of the development process is to eliminate variables and establish consistency. Keep at it.

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I have read the posts on shooting techniques here on the forum as well as on the net. I really dont suspect that is an issue here as I am consistant in supporting the rifle under the action on a rock steady rest and my contact with the gun is minimal,and I exersise the same practice every time, even though "touching the barrel" or other things warned against never seemed to make a difference in my groups in that given session. In the beginning, I deliberatley executed these practices to see if I could blame it on this. I guess I have to ask, in touching the barrel or holding the gun certain ways, will this, can this or might this affect the way the gun delivers groups? Is there any absolutes? Maybe it will affect one gun and not the other? Are we then to assume that a quick shot off hand will not impact at the same point as it would on the bench (other than for obvious reasons, you're not on the bench) so as to say the group we remember this gun to have yesterday on the bench "will" not or "may" not shoot the same in a hunting situation. I'm trying not to major on the minors, maybe I'm expecting to much? (this is good stuff)

i would think that a lot of this would have to do with
do you sling up in the field?
is your barell bedded, free floated?
do you use a soft or hard rest on the bench
are you shooting a lever action , bolt , or
single shot?
just have to work a gun over ask for suggestions [free advice] and see what you got likes

thats why guys who care do all this stuff

Smitty357,

You've asked several questions that pretty much get to the heart of this number of shots question. Here's the crux of it: When is one source of error obscuring another and how do you tell? Let's suppose, for the sake of argument, that you have an isolated source of random error that, if everything else on the gun and ammo were absolutely one-holer perfect and no other source of error existed, would open your group from 0.0" to 0.5" center-to-center on average. If you shot perfectly, you would see holes whose centers typically stayed inside a half inch circle. Now, let us further suppose you have isolated a second source of error that, when the first source of error is removed, also opens an otherwise perfect one-holer group up to an average of 0.5". If you allow both sources of error to operate at the same time, do you now get 1.0" average groups?

The answer is no. If the distributions are random, you will only get 1" groups when the two sources are randomly unilateral, or additive. The probability of that coincidence is not high. Probability theory shows the standard deviation of error (average group size) will be the geometric mean of the size of the errors caused by the individual error sources. This is described by Harold Vaughn in his book, Rifle Accuracy Facts (p.p.75-76, 2000 ed, Precision Shooting, Pub.). Vaughn was the supervisor of the Aeroballistics Division of Sandia National Laboratories and "is considered the "grandfather" of of the aeroballistics/flight mechanics technology base for nuclear ordinance at SNL". He has many other credentials, but the bottom line is that he is a ballistics expert of some stature and, happily for us, a shooting and hunting enthusiast.

Going back to my example, if we have two half inch average error sources, they will produce average group sizes of √(0.5²+0.5²), or about 0.707". Cutting out one of the half inch error sources will only reduce the average group size by 0.707-0.500, or 0.207".

Now let's suppose we have 5 sources of average error all equal to half an inch, one of which is your finger on the barrel. Average group size will be √(0.5"²+0.5"²+0.5"²+0.5"²+0.5"²) or about 1.12". When you remove your finger this drops average group size to √(0.5"²+0.5"²+0.5"²+0.5"²) or 1.00". Is there any wonder you couldn't tell the difference? How many shots would you have to fire to get an average that clearly showed that 0.12" difference with an acceptable degree of confidence? That depends on your definition of acceptable confidence. I gave the earlier suggestion of a minimum of 30 shots. Vaughn doesn't find that quite adequate. On page 235 of the same edition of his book I cited above, you find:


So, he likes to see 40 to 50 rounds fired. 25 is where he thinks he can begin to identify significant confidence. That isn't far from my old company's statistician's basement bottom minimum of 21. The difference can be accounted for by what the two men consider identifiable significant confidence. There is, obviously, room for opinion there, but not a lot of room (4 shots worth).

None of the above is anything a shooter wants to hear, really. It represents what seems like a lot of testing for one load. But, if you followed the reasoning, it will make sense to you that people who rely on smaller data samples often are vexed by unexplained fliers in the midst of otherwise good groups. Much cursing at the bench is the result of this, but it isn't really surprising that it happens. They just haven't ever proved the gun and load combination adequately for their own confidence requirements, and just don't know it.

As to different positions, they can affect POI. Probably the easiest way to see this is to put a sling on a stock that is touching the barrel, then check the POI shift when you sling up tight. You can measure it easily. Boots Obermeyer pointed out that some loads in some rifles seem to be more immune to shooter position than others, even if they were equal off the bench. It is a test most field and position match shooters fail to make when they work up loads. You want to find a few good shooting loads on the bench, then identify the one that gives you the smallest groups and the least POI shift from the different positions you will actually shoot from.

And yes, that means more testing.

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WOW ! this bullistic theology is deep to say the least. If you had to shoot at least 30 rounds to trust a load, by then the barrel is dirty only revealing more possiblility for error. If you clean in between, then how much do you shoot untill you can start trusting again? Makes me wonder if any or all of the 1 inch or under groups I shoot are just another error that I had'nt calculated in to the equation. And the groups you boasted how your bullet bucked the wind, maybe it is the wind you should thank for not revealing your poor posture that day, or maybe the wind kicked up just before the last shot, and hid a flyer that on a sunny day would have been revealed. And to think that if I ever achieve "accuracy narvana" I can only saver it for the now, for tomorrow 1 of 50 variables may stand in the way of a tight group. When the rubber meets the road and all considerations are made, can a load ever be trusted? Thanks to everyone for responding, this sheds a lot of light on the subject. Keep the replies coming, I am learning a bunch. Headed to the shooting bench, (and I'm still smiling) Steve

Part of the answer to your concern is that only relevant data need be included in the sample. Do what benchrest shooters do: clean every 10 record shots and fire two or three fouling shots or sighters between record shots that you don't count in your groups. This way, nothing counted in the group is fired from either a completely clean or a badly fouled barrel. If you check the link I posted earlier on Dan Newberry's round robin method, you'll see that one of its purposes is to distribute the cleaner and dirtier barrel shots among all the test groups as evenly as is reasonable to do. If you are using the gun to hunt and expect clean kills from a clean barrel with one shot (presumably, that's most of the time), then you can stop and clean after every shot during group testing so you know how your clean barrel groups.

As to whether you can ever trust a load, that answer is sort of like the words to the song where, after every decade of marriage, the author opines, yet again, that just maybe its going to work out? The question is, what level of confidence do you need? 90%, 98%, 99.9%? The more you shoot without a problem, the higher it gets. Most of us who think about defensive semi-auto handgun loads will fire hundreds of samples of a candidate carry round before we are confident enough in its feed reliability in our pistol.

For rifle accuracy, I think Harold Vaughn's statement that there is seldom any need to fire over 50 test rounds is pretty reasonable. If nothing went outside your required precision in 50 rounds, it is unlikely to give you a future problem under those same conditions. If you want to be clever, break the test up into groups of 5, as Vaughn did, and fire them under different temperature conditions. You can do that by keeping some against your body inside a coat or jacket, and some in baggies in a foam cooler surrounded by wet ice. Try alternating cold and warm round groups. Don't let the cold rounds sit in the chamber much over 15-20 seconds before firing, and the powder won't have time to heat up. Let the gun cool with the breech open for at least a couple of minutes between rounds, and that will help keep it all honest.

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"First contemplation of the problems of Interior Ballistics gives the impression that they should yield rather easily to relatively simple methods of analysis. Further study shows the subject to be of almost unbelievable complexity." Homer Powley

what all this adds up to is shoot a coouple of loads that you heard work or what powder and bullits
that you know work on game.etc mess with them some
and shoot how you are going to shoot
you will decide if you want to make some small changes to your technique or load as you go along

i have figured out that if i sight in for my wife i get the rifle to shoot then move the sights 2" to the
left and she is almost always right on the mark.

my bro-in-law shoots just to the right of me 1/2 inch or so and just a tad lower.

but you do not know this stuff without the trigger time