FILED BULLET BASE ACCURACY

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joeb33050 posted this 4 weeks ago

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joeb33050 posted this 4 weeks ago

 

4/26/2006   M54 Winchester 30WCF, 30X STS, 12/AA#9, WLP primers, CF Ventures Soft Gas Check, 308403 lubed Darr + beeswax, muzzle clamp/anti-cant device and flat bench rest. 65 bullets had 45 degree filed bases to about half the height of the base band. A set of 18 cases had file marks put on the base and rim for orienting. A fouler was shot before each set of shots, at the center dot. Bullets were put in the cases with the filed bullet marks at 12, 3, 6 and 9 o'clock, four shots, and the cartridge was put in the chamber with the case base/rim mark at 12 o'clock. Then as precisely as I could put the bullet in the case and then the cartridge in the gun, bullets/filed bases were oriented each shot.

 

Four with filed bases, four perfect bullets, then four with filed bases and four perfect bullets; with a sighter comes to 17 shots per fifteen-minute relay. 64 shots each with filed and perfect bases were made. All shot at 100 yards.

 

The weather varied from sunny to rain, still to very windy. In the still sunny conditions there was a lot of mirage, and biting horseflies about the size of robins. Lots of "damn"s and slapping body parts.

 

The damaged base group is  3 9/16" high by 4 11/16" wide, with no discernable pattern. The perfect base group is 2 7/8" wide by 2 1/2" high with the center shot out and outliers ~evenly distributed.

 

 

 

It is clear from the target that bullets with damaged bases do not shoot wildly, that many of the bullets cluster into a small group, and that the group/distribution is not doughnut shaped. This suggests that the mechanism decreasing accuracy is not one that operates every shot, but is probabilistic in nature.

 

 

 

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nosee posted this 4 weeks ago

That is what I,am, probabilistic, by nature.

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Ross Smith posted this 4 weeks ago

don't know what the empirical data says but my rational side like the perfect base group better.

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Ken Campbell Iowa posted this 4 weeks ago

hey joeb the data man ... since my comprehension of formal statistics tapers off rapidly after about standard deviation ... and sigma quality of prediction ...

if we used mean radius of shot placement wouldn't the data be more valuable ??  more predictability with fewer shots ??

it seems to me that using group data is more of a game that pretty much wastes 8 out of ten shots ....  surely 9 shots in a hole with 1 shot 3 inches away means something more than 10 shots all 1.5 inches from the group .

i realize that measuring groups is much easier ... but shouldn't groups be at least 100 shots to reach 80 per cent confidence if you only measure 2 of them ?  i do realize that 100 per cent of entrants DO NOT win the power ball .  my kids do not realize that .

 

******************

btw, jim scearcy has a neat little excell sheet where you enter the co-ordinates from any desired fixed point and it gives you mean radius of the group ... also if you want  it creates a graph of the group ...  i for the challenge of it added a programmer's nightmare crutch to give group size from those entries ... but just on my copy .  there are even outside commercial programs available where you just enter a photo of the group and BAM! the numbers spill out .

***************

and thank you for the tons of time and energy and ... work !! ... you have put into solving the accuracy problem for the rest of us .  much appreciated .

ken

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joeb33050 posted this 4 weeks ago

hey joeb the data man ... since my comprehension of formal statistics tapers off rapidly after about standard deviation ... and sigma quality of prediction ...

if we used mean radius of shot placement wouldn't the data be more valuable ??  more predictability with fewer shots ??

it seems to me that using group data is more of a game that pretty much wastes 8 out of ten shots ....  surely 9 shots in a hole with 1 shot 3 inches away means something more than 10 shots all 1.5 inches from the group .

i realize that measuring groups is much easier ... but shouldn't groups be at least 100 shots to reach 80 per cent confidence if you only measure 2 of them ?  i do realize that 100 per cent of entrants DO NOT win the power ball .  my kids do not realize that .

 

******************

btw, jim scearcy has a neat little excell sheet where you enter the co-ordinates from any desired fixed point and it gives you mean radius of the group ... also if you want  it creates a graph of the group ...  i for the challenge of it added a programmer's nightmare crutch to give group size from those entries ... but just on my copy .  there are even outside commercial programs available where you just enter a photo of the group and BAM! the numbers spill out .

***************

and thank you for the tons of time and energy and ... work !! ... you have put into solving the accuracy problem for the rest of us .  much appreciated .

ken

Thanks, Ken;

If shot location is Normally distributed-and it seems to be, then there are any number of measures of the group that are mathematically related to each other. 3 shot group size and 7 shot mean radius are related such that 3 shot group size times some number = 7 shot mean radius. With 7 shot groups, or any number of shots, every shot contributes to the measure. Any sensible measure defines a host of other measures. 5 shot groups have a mean radius = .34 X group size.

I have an EXCEL workbook explaining this, if you wish.

joe.b.

 

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Ross Smith posted this 4 weeks ago

 So, if the purposely damaged bullets are only slightly affected, how does that compare with wrinkly as cast bullets? Are we wasting our time culling those?

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joeb33050 posted this 4 weeks ago

 

3.7.1 WRINKLED BULLETS AND ACCURACY

 

 

 

By John Alexander

 

Over the years I have often wondered how picky I should be when inspecting a freshly cast bunch of bullets.  For various reasons a few will have gross defects that obviously rule out trying to shoot them.  On a good day with a good alloy, a good mould, and everything working right almost all the bullets will seem to be perfect by the unaided eye.  But they aren’t perfect.

 

If you examine them under a stereomicroscope at say 20X you will see that many are considerably less than perfect.  Should we sort our bullets with the help of a microscope?   Most of the top competitive shooters in the CBA don’t sort with a microscope and they still manage to shoot some amazing groups, it seems safe to say that a microscope isn’t needed even though visually “perfect” bullets may not look perfect under magnification.

 

So our usual criteria for good or bad bullets is arbitrarily based on what the human eye can see without aid.  Is this arbitrary limit the proper one to determine what bullets should be rejected?  If a skilled shooter had poor eyesight and couldn’t see defects as well as the average shooter would that be a disadvantage, I don’t think we know.

 

Although casting is fun when everything is working smoothly and the bullets are nearly flawless, on some days the cast bullet gods seem to punish us with bullets having rounded edges or wrinkles of various sizes –or both. Even after repeatedly cleaning a mold, turning up the temperature of the pot, adding tin, fluxing with a magic elixir, and whispering ancient incantations passed down from the Schuetzen shooters in old Bavaria, as well as some more modern expletives, I sometimes wind up with a number of bullets with easily visible wrinkles or rounded edges.  The advice usually offered is to remelt all such bullets, or at least cull them out to be used only for shooting offhand or for fouling shots.

 

I like to cast bullets but I like to do some other things with my time even more and after I have spent a couple of hours casting I am reluctant to throw away a substantial fraction of my production even if they don’t look perfect.  I have always wondered how severe a defect has to be before it makes a difference? Logically the standard should depend on what the bullets will be used for and how much precision is needed.  If they are to be used for offhand or casual pistol shooting, or in a rifle that only averages three minutes of angle it seems reasonable that we should be able to relax our standards a bit compared to the standards needed for competitive benchrest shooting or squirrel hunting.

 

It has also been argued that the size of the bullet also matters and that defects in small bullets will cause more dispersion than similar defects in larger bullets. This alleged relationship has been cited as a reason why it is considered more difficult to attain good cast bullet accuracy with the 22 bore than with larger calibers. This seems logical but as Ken Mollohan argued in Fouling Shot #212, logic based on faulty assumptions can lead one astray.

 

Over the years I have occasionally run limited tests comparing “defective” bullets to “good” bullets and have been surprised at how well some of the defective bullets shot in a direct comparison.  Many other experienced shooters have observed similar results and are more tolerant about what bullets are good enough for the intended purpose.

 

Cast bullet shooters, and especially beginning shooters, need some realistic advice about how to judge when a bullet should be rejected.  I believe the standard advice that bullets with any visible defects should be remelted is not only arbitrary (as noted in the first three paragraphs) but also often wastes a lot of perfectly good bullets as well as a lot of casting time and effort for no good reason. More importantly, the zero tolerance rule pushed on beginners may cause them to give up casting in frustration when they could be getting good results with less than perfect bullets.

 

One difficulty in developing better advice for beginners is in describing the level of defect.  How do you describe what a small or large wrinkle is or how much rounding of edges is enough to make a difference.  I have a lot of records of past tests that show that bullets that were “slightly wrinkled”, or had “moderately rounded base edges” or “badly wrinkled” either did or didn’t do as well as the “good” bullets when fired in alternative groups.  After a few years those notes aren’t very helpful even to me and they certainly aren’t useful to other shooters. But just because describing the level of defect consistently is difficult doesn’t mean we should give up.

 

Photographs may be one way of describing defects.  I recently had the opportunity to try this method when I cast a batch of 75 grain 22 bullets.  The bullets were of scrap lead of uncertain composition with a BHN of about 15.  Out of the 119 bullets about 30 had one or more random wrinkles that looked bad enough through my trifocals to make me reluctant to shoot them in an upcoming postal match.  I called them my culls.

 

I picked out six bullets that were typical of the culls, rubbed black ink in the wrinkles to make them show up better, and took the accompanying picture.  I then loaded the bullets in the picture along with 24 additional similarly wrinkled bullets.  As a control, I also loaded thirty visually perfect bullets, from the same batch. The load was five grains of 700X ignited by a Remington small pistol primer.  The bullets were lubricated with LBT blue.  The average velocity ten feet from the muzzle was 1,430 fps.

 

I shot the 12-5 shot groups in my 223 Tikka Lite on the same day in a tunnel. The six five shot groups with the culled bullets were shot alternating with six five shot groups with “good” bullets to avoid systematic differences caused by bore condition, fatigue, or other variables. The six groups with the wrinkled bullets averaged 0.78 minutes of angle and the six groups of “good” bullets averaged 0.82 minutes of angle.

 

I was not surprised to find that the wrinkled bullets appeared to shoot as well as the good bullets because in past tests bullets with similar wrinkles had averaged better accuracy about half the time.  Note that the accuracy difference was NOT statistically significant.  I am not in any way proposing a new theory, similar to the one justifying the dimples on golf balls, that wrinkled bullets are more accurate.  I don’t believe they are.  But it apparently will take a test with a rifle/load combination more accurate than the one in this test to show that they are less accurate.

 

One thing is clear.  If your rifle is shooting two inch or larger groups it is unlikely that results can be improved by discarding bullets with wrinkles similar to, or smaller than, the ones in this test.  Changing other factors such as bullet fit, alloy hardness, or powder type or charge are more promising tactics than more critical sorting of bullets.

 

This was a limited test with a specific caliber, bullet, load, and rifle and may not apply for all situations.  However, because the 22 caliber is alleged to be sensitive to bullet defects, wrinkled bullets may have even less effect on larger calibers.

 

It is also worth noting that the rifle had a one in eight inch twist, instead of the one in fourteen inch twist of most 22 centerfires. According to prevailing theory, the quick twist should have accentuated the effects of the undoubtedly unbalanced bullets.

 

I hope this test and the accompanying picture will be of interest to readers and provide food for thought.  I also hope others will be encouraged to run similar tests with other types and levels of defects and report their findings.  I suspect we usually spend too much of our time and attention sorting bullets when we should be looking elsewhere to cure our troubles.

 

 I know that many casters take pride in how their bullets look, as well as how they shoot, and will not be interested in shooting wrinkled bullets even if they shoot well.  They should keep right on discarding those ugly bullets.  After all cast bullet shooting is a hobby, not a way to save civilization, and we should do it the way we enjoy doing it.  However, for those like myself who are a bit lazy and would rather shoot than remelt and recast bullets this article may offer bit of guidance about how some easily visible wrinkles can be ignored with no loss of accuracy.

 

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joeb33050 posted this 4 weeks ago

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GP Idaho posted this 4 weeks ago

 This is what got me reminiscing in John A.'s post I  got to the party somewhat late, just about the time Ken M. left us. I have read a lot of what he had to say about our craft and can't think of any of his observations that I disagree with.  I miss Molly. RIP

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Ross Smith posted this 4 weeks ago

Thanks Joe! That cleared up some of my questions.

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Ross Smith posted this 3 weeks ago

speaking of filed bullet bases, has anybody tried squaring-trimming the bullet base in a lathe??????????????????

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Ken Campbell Iowa posted this 3 weeks ago

yes, and it made a       significant      improvement in mean radius.   i cut some both square and some beveled ... both improved grouping.  the beveled without gas checks.

however, i think my castings needed improved bases ..... if the castings had been perfect " enough " as cast ... they likely would not been improved much .  hah i had to say that .

i used a lathe collet but for more than a few a bullet swage/bumper is less finicky ...... both methods require a little practice ...   the collet can crimp the soft lead  and unless the swage moves the lead, it might not make a perfect base and seat the gas check perfectly ...

ken

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Ross Smith posted this 3 weeks ago

Good to know. The original Mr. Hoch of Hoch molds claims the base as the most important part of the bullet, hence his nose pour molds. I also have noticed less than square GC's on my bullets after crimping so I went to the NOE method of "squaring the check " before crimping. Seems to help me. 

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Larry Gibson posted this 3 weeks ago

John

 

At what range was that test conducted in the "tunnel"?

Also I note your load was running at 130,500 RPM.....just sayin is all.........cool

LMG

Concealment is not cover.........

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John Alexander posted this 3 weeks ago

It was a 50 yard tunnel.  So the actual average group sizes were 0.39" for the wrinkled bullets and 0.41" for the " good" bullets.

John

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GP Idaho posted this 3 weeks ago

Ross;  Another fan of the NOE check seating die here. I started with the NOE expanders that fit the press ram like a shell holder but that was so-so as to getting them set just right. Even with checks so tight that I can't get them on with my thumb, the seating die gets them mounted perfectly. Gp

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Old Coot posted this 3 weeks ago

I remember an article in the Rifleman Oh, circa 1965 more or less about  bullet damaged bullets and how they shot.  The nose and sides would still perform like the original despite having up to 5 grains removed by a file.  However, when the bases of  the pulled GI 30cal. bullets were filed accuracy went to pot in a hurry.  I don't remember the figures or quoted group sizes, but it was very evident the messing with the base was not a good thing.

Good luck with you experiments.

 

t

B.E.Brickey

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Hoppy posted this 1 weeks ago

I generally agree with the old saw that says it's the base of the bullet that does the steering, and when I cull bullets it's usually because there are significant base flaws. I once built a "bullet base truer" that consisted of a swing arm with a precisely vertical piece of angle aluminum at the end. Hold the bullet in the corner of the angle and swing it back & forth on a piece of emery paper until its base was perfectly flat and perpendicular to the axis of the bullet. It worked perfectly--except that it didn't, because there was no discernible difference in the accuracy of the modified bullets versus those with untrued bases. That experimental device is now hanging on the wall gathering dust. The bullets I was experimenting with, by the way, were all .45s for use in .45-70 and .45-90 rifles. On to the next theory. . . .

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rmrix posted this 1 weeks ago

John

 

At what range was that test conducted in the "tunnel"?

Also I note your load was running at 130,500 RPM.....just sayin is all.........cool

LMG

______________________________________________

The RPM reference must be inside knowledge. 

 

my 2 cents worth, I have completely stopped weighing match bullets and only look at the base edge while casting to cull. Looking at my long term scores, nothing has changed since making this change. This supports what I read above.  Improvements in my match scores need to come from (even) more wind reading and trigger time.

Just shoot more ;-)

The above does not apply to group shooting as much. Cutting a 1/2 inch off my 500 meter or 1000y group, as if it could be isolated, does little for my score.

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Ken Campbell Iowa posted this 6 days ago

just a thought on correcting bases /checks by swaging ... it occurs to me that you have to fully swage a bullet while reswaging an uneven base ( or nose etc. ) ...   or the extra metal just randomly goes to another unbalanced location ..

but i have no data to back this up ...

and sanding/lathe cutting .... bases would not carry this liability ..

i think ... maybe ...

ken

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