Can indexing bullets improve groups

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Last Post 25 February 2015

CBA President

John Alexander posted this 12 February 2015

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Indexing is certainly useful for telling which bullets came from which cavity when the cavities aren't alike. It is at least conceivable that in certain cases with really bad bullets that indexing may help shrink groups. But a lot of good shooters don't index bullets and win without doing it. Does anybody know of any systematic studies that give information on how bad (and in what way) a bullet has to be before indexing will show a measurable decrease in average group size? Is it instead just one of those things we blindly do because we read somewhere that it works. Or maybe do in the hope that the more trouble and time we take to reload groups will magically improve. My own tests were with bullets from a single cavity mold that was beagled out of round and in which the halves were offset more than .001". These defects made me think that indexing would help. The bullets were shot in a falling block rifle so I could easily and precisely index bullets. I shot a lot of groups but could detect no difference in average group size compared with not indexing. However, that was with one bullet design (similar to NOE 22570 RN) and in a rifle only capable of averaging about 1MOA for five shot groups. With different or worse bullet defects, or with other bullet designs, or at higher levels of precision, results might be different -- but do we know? Maybe we should try to find out. John

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45 Comments

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CBA Member

cheatermk3 posted this 25 February 2015

John Alexander wrote:

"...After finding the thin side and marking it with a cut in the rim, have you ever shot a test of a series of alternate groups with the case indexed in one orientation (say 12 o'clock) versus identical loads with the index mark randomly positioned (around the clock so to speak) to measure the benefit indexing cases by the thin side? “

Sorry not to have responded sooner but I lost track of this thread... To answer your question , John, No, I have not.

I don't mark the thinnest portion of the case wall for any reason other than wanting a “standardized” reference point. I could just as easily have used the thickest side; just wanted to be consistent.

My reasoning is that I'm striving to align the centerline of my loaded round as closely as possible with the centerline of the bore. I was using an RCBS concentricity gauge to indicate the variation in wall thickness.

I do not at present own a tubing micrometer (I just a few minutes ago ordered one from midway) but when turning my necks just enough to remove the “high” spots and having the portion of the neck that is un-touched line up with the “witness mark” cut into the rim told me I had indeed found the thin side.

Since I turn the necks after marking the rim I have none to use for the testing being proposed here.

I'm about to start prepping a lot of cases for match shooting and I will leave 12 cases marked but not turned.

When I get to that point, I'll try shooting a few groups for the testing Joeb is proposing.

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CBA President

John Alexander posted this 23 February 2015

Yesterday I discovered that I have a mold with .003” misalignment between the halves and .002” out of round. That should be a good bullet for trying indexing. I will see if it will shoot in my Ruger #1 so I can index well.

John

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Standard Member

TRKakaCatWhisperer posted this 21 February 2015

Snow and ice here in VA. When it melts ....

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CBA Member

billglaze posted this 21 February 2015

I'd be glad to help out on this project. Just lay out the required parameters/conditions and I'll be good. I'll have to shoot some? Well, I'll just grit my teeth and carry on. Rotten job, but somebody has to do it. I'd really like to omit a lot of the items that I started under the “monkey see, monkey do” mental conditioning, but I keep coming back to them under the logic banner of “well, maybe it doesn't do any good, but it can't hurt." Sure like to have some hard proof that I could omit at least some of the procedures. Bill My eventual goal has to eventually come up with loads/procedures that will me allow me ti have sub-moa competitive groups while loading with my Dillon progressive presses. May be an unreachable goal, bit I'll keep striving.

In theory, there's no difference between theory and practice. In practice, there is. My fate is not entirely in Gods hands, if I have a weapon in mine.

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CBA Member

RicinYakima posted this 21 February 2015

Me too, as I am getting ready to start practicing for the matches in June. Ric

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CBA President

John Alexander posted this 20 February 2015

Be glad to shoot three pairs of 5-shot groups. 18 more volunteers needed.

This shouldn't require much work for shooters already indexing and are curious.

I will be glad to shoot more pairs is we are a little short of volunteers.

John

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CBA Member

RicinYakima posted this 20 February 2015

Joe, You only need 19 others. I will shoot 6 five shot groups for you. Ric

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Standard Member

adrians posted this 20 February 2015

John Alexander wrote: adrians: I think you are right about the purpose of the indexing mark. It is hard to know but I believe a substantial percentage competition shooters index and some non-competitors as well. John
Thanks John , I thought I was on the right track . I don't breach seat nor index , wouldn't know where to start but I think the subject is very interesting and you guy's have enlightened me about all these funny looking dimples on a couple of my molds. All I know is the one in the pic shoots pretty good out of a couple of my 8mm's. Thanks guys.

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CBA Member

joeb33050 posted this 19 February 2015

OU812 wrote: Bullets should also be indexed in sizer before sizing and seating gas check.

I always size nose first in my RCBS Lubramatic using hollow nose punch to square check at bullets base. Then finish pushing bullet thru sizer die using square face sizer stem to prevent nose distortion of bullet.

Lately I have been experimenting with pan lubing and hand dipping to prevent bullet distortion.Ya know, I scored a really big pail of wheelweights for only $3.61!!!Anyone know if you can shoot gas check bullets without the gas checks? Is it legal in CBA competition?

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Standard Member

OU812 posted this 19 February 2015

Bullets should also be indexed in sizer before sizing and seating gas check.

Lately I have been experimenting with pan lubing and hand dipping to prevent bullet distortion.

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CBA President

John Alexander posted this 19 February 2015

adrians: I think you are right about the purpose of the indexing mark. It is hard to know but I believe a substantial percentage competition shooters index and some non-competitors as well. John

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CBA Member

joeb33050 posted this 19 February 2015

John Alexander and I have been proclaiming the heresy that “the name of the game is the same” is not true; that controlling variables to precise tolerances and performing uniforming operations does not markedly reduce group size. Weight-segregating primers and/or peening extractor grooves to .0005” tolerance ain’t going to do it.
I’ve been estimating the number of groups that must be fired to attain varied confidence level/% difference levels for over 25 years. None of my solutions is absolutely correct for arcane reasons, but they’re close and sum to: It takes a lot of groups to be very sure of a small difference in group size.

John, and I with less enthusiasm, recommend experimentation, analysis, recording and reporting. It isn’t happening, and it’s not going to happen. The number of groups required, the religious fervor of the powder-weighers and the dogmatic belief of the “all guns are different” chanters discourages experimentation.

There is another approach.

Imagine that there were some cast bullet shooters willing to do a little experimenting, and some others willing to sum and analyze the results, and yet some others willing to organize.

Imagine that we wished to know if indexing bullets reduced group size, that there were 20 shooters willing to shoot three groups indexed and three groups not indexed and report the results.

We would have 60 pairs of groups, indexed and not; enough to analyze and make some statement.

This would get us over the large-number-of-groups hump.

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Standard Member

adrians posted this 19 February 2015

This has been an interesting discussion, me knowing nothing about indexing but own a indexed mold. I can see the advantage of marking one cavity of a multiple cav mold to indicate your “best bullet cavity” but this one is a single cavity mold and I'm told its a tapered bullet so maybe this was indexed to be breach seated at 12.00 every time,,,, Am I way off here ,? I don't mean to hijack if so ,sorry.

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Standard Member

TRKakaCatWhisperer posted this 18 February 2015

John Alexander wrote: ... Is there a type of defect that shows up in the same location relative to the parting line of the mold so indexing might help?

...

Yes! Joe's going down the right path in sorting out whether or not there is a detectable difference among a given set of bullets when they are or are not indexed. Good research.

Next question which you raise here is slightly different; additional tests can measure the effects of size and location of specific defects. What size of defect (simulating a void) is detectable? And then, as the size is varied, at what point does the effect become measurable on the target?

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CBA President

John Alexander posted this 18 February 2015

In my opinion any serious shooter who really wants to find out if changing something really changes group size or if the two groups he is staring at are just an accident and the next two will give the opposite answer, should copy Joe's little table and use it. When you think you see a difference between two powder charges, two primers, two seating depths, or between indexing or not indexing, etc. check the table and see how many groups you have to fire to be fairly sure it isn't just natural variation that makes the first two groups show a difference. Everybody should be able to understand the table. No complicated calculations. No computer needed. Using it would help us avoid thinking some goofy procedures somebody thinks up is real and would keep us out of a lot of blind alleys, or up the wrong alley and wasting our time. Where we no spend a lot of our time.

This doesn't automatically mean that you always have to shoot lots of groups to be fairly sure that the difference is real. You only need lots of groups if the difference is small. As the table shows, if the difference is 20% four pairs of 5-shot groups will give you pretty good assurance that you are on to something not just looking at the normal variation in group sizes.

For instance, the several hundred percent improvement Marshall claimed for indexing in Col. Harrison's “Cast Bullets” would probably require only one pair of groups to be pretty sure it was true.

John

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CBA Member

joeb33050 posted this 18 February 2015

This is approximate for 5 shot groups.

If the hypothesis is: There’s a difference in group size when we do or don’t index.” , and we’re indexing both case and bullet, then we need to shoot some number of groups to test this hypothesis-some indexed and some not. One group each is a “pair” ..

Now, how many groups must be fired to test the hypothesis?

One of the ways to get a guess at the number of groups that should be fired is using the “paired difference” t test. I solved this for n for several levels of confidence:

The number of group pairs that must be fired depends on 2 things: how confident you want to be in your answer and the % difference in pair averages.

If we want to be 90% confident that our answer is right, and the average difference between group sizes is 5 %, we need to shoot more than 30 pairs of groups, more than 60 groups.

90% confident, 10% difference, 13 group pairs

90% confident, 15% difference, 7 group pairs

90% confident, 20% difference, 4 group pairs

95% confident, 10% difference, 21 group pairs

95% confident, 15% difference, 10 group pairs

95% confident, 20% difference, 6 group pairs

97.5% confident, 10% difference, 29 group pairs

97.5% confident, 15% difference, 14 group pairs

97.5% confident, 20% difference, 9 group pairs

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CBA President

John Alexander posted this 18 February 2015

Joe,

Sorry that my original question was not clear although you have it right. In hindsight I should have only asked the first question. -- Does indexing imperfect bullets ever improve group size.

I made it too complicated. My testing always failed to show that it helped and apparently your's didn't find any improvement either. I was hoping that somebody had had positive results since so many folks are spending the time doing it.

"Now these imply that that accuracy increases happen when imperfect bullets with varying types and magnitude of imperfection are indexed, and I don't know why anyone would suspect that this would be the case."

I agree that if the imperfections are varying in types and magnitude and location it would be strange to think that indexing might help -- and this describes most defects we talk about. Is there a type of defect that shows up in the same location relative to the parting line of the mold so indexing might help?

Your suggested protocol for testing the indexing of both bullets and cases would work but It would be start if shooters would just test whether there is any actual bullet defect that can benefit from indexing. As it stands now, as far as I know, there is no such evidence.

John

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CBA Member

Ken Campbell Iowa posted this 18 February 2015

creighten audette american rifleman june 81.

benchresters do not always agree on this result; however most will prefer the most consistent brass available; usually lapua.

” question everything “

ken

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CBA Member

LWesthoff posted this 17 February 2015

I don't know whether indexing/orienting can be shown to help accuracy - but I do it, and here's why: Nothing can be made perfectly. If there are imperfections in my rifle's chamber, in my bullet mold, in my sizing die and/or in my seating die, then if when I am casting, sizing, seating and chambering I always orient everything in the same way (as precisely as I am able) when I am testing for an accurate load, and then when, after choosing a load, I shoot it in competition, I figure I have something that works in MY RIFLE, machining errors notwithstanding.

I have neither the time nor the money to test all these things to see which ones do, and do not - affect accuracy. so I try to always do each thing the same way every time. Then when I find something that works, I can do it again.

Makes sense to me.

Wes

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CBA Member

joeb33050 posted this 17 February 2015

Fortunately for us all I’ve been tutoring a lady who is taking Statistics 2, and I’ve been working hard to stay just a few pages ahead of her. I’ve been strongly emphasizing the importance of precisely defining/stating the hypothesis that’s under discussion.

I’ve read John’s original post a dozen times, trying to understand the question/s; here’s what I think he wants to know:

(Indexing, here, means that the item is oriented in a certain way, axially.)

Does indexing imperfect bullets reduce group size?

What is the type and magnitude of bullet imperfection threshold where group size reduction begins?

Now these imply that that accuracy increases happen when imperfect bullets with varying types and magnitude of imperfection are indexed, and I don’t know why anyone would suspect that this would be the case.

It implies, for example, that as base-to-long-axis perpendicularity varies from 90 degrees, that as the smaller angle approaches some number, indexing bullets reduces group size. Example still: as the smaller angle reaches 84 degrees indexing reduces group size 10 percent.

I don’t know why this question, nor how to test the premise.

There is another question that might be of interest and more easily tested:

Does indexing bullets, cases, or both reduce group size?

We could combine the three in the design of the experiment, thus:

Shoot n r groups with cases and bullets oriented randomly

Shoot n b groups with the bullet indexed and the case oriented randomly.

Shoot n c groups with the bullet oriented randomly and the case indexed.

Shoot n bc with both bullet and case indexed.

Compare group sizes.

We must keep in mind that indexing anything by eye and hand is not an extremely precise matter. Keeping a dot on a bullet aligned with a v in a case rim, and the v on the case rim aligned with 12 o’clock in the rifle chamber is a process frought with opportunity for error. Keep in mind that on a clock with hands, one minute = 6 degrees. A guess is that alignment of that v is possible with a precision of +/- 6 degrees.

So this might be on the way to designing the experiment to test the hypothesis that alignment reduces group size.