When do Bullet Defects Make a Difference?
In the thread “Casting with Lyman Molds” Joe Brennan recently mentioned that he had 40-50 rejects in casting a batch of bullets and that he didn’t know why. Joe says he sorts under magnification so that started me wondering how bad those bullets were and if they would have shot just as well as his “perfect” bullets.
When I started casting I used to get a lot of less than perfect bullets and on some days I still do. Being a depression baby, I don’t like to throw things way and when I got curious and shot the “rejects” against my “perfect bullets” they seemed to shoot just as well. I reported on one such experiment with badly wrinkled bullets in TFS #213 in which the wrinkled bullet’s 5-shot groups averaged .78 MOA and the good bullets averaged .82 MOA. I have tried similar tests several times and haven't found a difference as long as I don't shoot the really gross defects -- parts of a band missing etc.
Joe rejected only about ten percent and throwing away ten percent isn't too painful even for me, so maybe this issue doesn't make much difference to experienced casters. But for beginners that rejection rate may include most of their bullets if they believe that any little wrinkle or slight rounding of sharp edges, or bump on the bottom must be remelted. And that’s what we usually tell them because we don't know ourselves. That may be one of the reasons that beginning casters get discouraged and quit. Early success is important in sticking with a new hobby. If we want more CB shooters we should avoid discouraging them unnecessarily.
What do we know about the importance of defects? I think not much. I hope others, out of curiosity, will compare how their rejects shoot compared to their “perfect” bullets and share their results. We have been at this business for several hundred years and really should know more about the importance of defects by now.
John
How Perfect Should a CB be?
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The "Speaking Frankly" 30-06 article in the Lyman CB manual has volumes to say about perfection of cast bullets. Only a careful sorting of bullets was going to be enough for Frank. Lesser bullets had their place, but only for practice. Really imperfect ones went back to the pot.
However, a recent test showed that the shooter has more to do with accuracy than does the bullet. I matched jacketed bullets at the same velocity as cast and my scores were not any higher. Seeing the sights and holding steady had more influence than did the individual bullets. Just my two cents.
Dave
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Want to shoot better scores? Practice more!
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If the bullets are equally “flawed” around the whole bullet, and the diameter is correct, and the base is uniform, the effects could be minimal. Bullet weight does impact longer range trajectory though, and could cause erratic points of impact. I totally disagree with Mike Venturino that flaws are immaterial and that you can shoot anything you get out of the mould. He's primarily speaking about handgun bullets I believe, but I think his performance standards for most bullets are far below my own. In the same issues of whichever magazine he's working for, you can see him get really fussy over his black powder rifle casting, so I know he knows the difference.
My standards are the same for any bullet I make. They need to be of the highest quality I can produce.
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On the fence on this one. Not so much the testing of the good, the bad and the ugly at long distances. But more of an inconsistency at the bench when we experience the “this load shot good a few days ago but today it stinks” conclusion. We need to look beyond the so called inconsistency of the quality of the bullets and look in the mirror and convince ourselves that our bench technique is repeatable day after day. Failing that bullet quality takes a way down the list second seat.
Tom
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Life is too short to compete with imperfect bullets. The easiest variable to eliminate, particularly in the PB class. If the base is good, the bands square, and no wrinkles, they go into my score box sorted into 1 gr weights. I'd rather spend my time doping wind and mirage than wondering if that “marginal” bullet cost me that 10 or X. C'mon, a glance will tell the tale, if it is not good in your heart of hearts toss it back into the reject can.
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Well from the jacketed world, try a bag of 147 grain M80 pulled from 7.62x51 NATO cartridges. A few blemishes but not too bad, weights however vary by +/- 2 grains. Load them randomly and they have about 4 MOA at 100 yards from a M1903 A3 with iron sights, shot prone with a sling. Sort them into weight groups and you can maybe get to 2 MOA. The control would be to not know what I was shooting (If I know their better maybe I shoot better?). The same rifle in the same conditions shoots well sorted cast, fitted to the throat about 2 MOA at 100. A factory modern rifle, with a scope and bench rested might make everything tighten up but I believe the trends would continue.
I am with Ric, if you make them, make them as good as you can and you will have better accuracy.
Dave
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There are a lot of people in the world who don't follow anybody else's procedures. As they have found, you might also if: while weight segregating, you also diameter segregate. That has produced some very interesting results in the lowly 22 Hornet cartridge.
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John, I have seen the exact results you describe and wonder why. I have tried all sorts of voodoo and still see variation. One day a near one hole group and the next not so much. I am making the best ammo I can and this is why I believe some of it is a head game, hence the idea of it is just as important as what you do. At least to me. Plus I just flat out enjoy tinkering with this stuff and never want to stop till I am cold and stiff. Great forum. Squid
"Squid Pro Quo"
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I should have added one more comment to the description of my test's above.
Of the 60 record shots fired one was disregarded I called it out when shot. It was the only shot that made it's separate hole. It would have made one of the groups of uniform weight bullets considerably bigger. A two oz. trigger takes some getting used to.
John
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What difference do bullet defects make? Not much if the range is short and/or the velocity is low. if you are shooting at longer ranges (100+ yards) and the velocity/RPM is higher bullet defects can make a huge difference in accuracy.
LMG
Concealment is not cover.........
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My standards are the same for any bullet I make. They need to be of the highest quality I can produce.
We are on the same page, pride of workmanship has a lot to do with what I keep and what goes back in the pot.
Guys that love to chronograph, keep saying the small SD's make smaller groups, yet I have never seen that on the target. Some do, but some don't make smaller groups. Same idea, what you think affects your outcome.
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Well said Tom. Folks go to great lengths to place the blame on small defects or this powder, that primer etc. All to get around the obvious, they have poor technique! No amount of fastidiousness in bullet prep. will overcome personal inabilities. That being a big part of why I shoot plates, gongs, and beer cans instead of benchrest targets. lol Gp
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Early in my association with the CBA I read some posts on this subject so decided to try my own test.
After a few of my first casting sessions I weighed several hundred bullets. I was able to assemble two sixty bullet test batches. Each batch had 30 bullets in the middle of the weight range, 15 of the heaviest bullets, and 15 of the lightest bullets, slightly less than 4 gn spread from heaviest to lightest. I shot five shot groups at 100 yards alternating between groups with the “perfect” bullets and groups with either two heavy/three light or three heavy/two light. In the end the “perfect” bullets averaged 1/4” tighter groups (1.24” vs 1.52").
Coincidentally, my first win was in an informal match shooting groups at 300 yards. The margin of victory was 1/4".
Of course as always there's “the rest of the story".
As anyone should be able to tell you (though many can't) for the results of any experiment to be valid they have to be repeatable. Through the summer the second batch of test bullets sat in a box while I prepared for matches and learned more about casting techniques, shooting techniques, etc etc etc. Finally on a reasonably nice December day I headed for the range with the second batch of bullets. I have no idea why but this time I could barely muster groups around three inches and the most charitable way I can put it is that I was unable to validate my earlier experiment.
In the meantime I have learned to cast more uniform bullets, use more uniform pressure when sizing, work with seating depth, etc etc etc. Even so, as the winter gets longer and colder, when some of those “honeydo's” come along, I may find it useful to have a large batch of bullets that really need to be sorted..>
John Carlson. CBA Director of Military Competition.
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What difference do bullet defects make? Not much if the range is short and/or the velocity is low. if you are shooting at longer ranges (100+ yards) and the velocity/RPM is higher bullet defects can make a huge difference in accuracy.
LMG
LMG
I suspect your first sentence is right. Any way it matches my test results.
Do you have any numbers to go with your statement that defects make more trouble at at longer distances? A certain size wrinkle or a certain radius rounding of the sharp edges will make a bullet hit about ___ inches or feet from the group center in at 600 yards?
What rotation speed will start to cause trouble? The bullets in my test reported in TFS #213 were rotating at 126,000 rpm so it must be higher than that.
John
There is indeed and RPM Threshold where accuracy goes south due to adverse affect increased RPM has on the imbalances (what defects in the bullet cause). With the ternary alloys we commonly use and the usual fast to medium burning powders the RPM Threshold will generally fall between 120,000 and 140,000 RPM. The things that push the RPM Threshold up are better bullet designs that fit the throat, better balance of antimony and tin in the alloy, less defects in the bullets (consistent bullet weight and shape), consistent loading techniques, a proper lube, a slower burning powder to lengthen the time/pressure curve and numerous others. If you do everything right you can push the RPM Threshold above 140,000 but at some point (the faster the barrel twist the sooner) you will cross the RPM threshold and accuracy will go south very quickly, especially at longer ranges as non-linear group dispersion occurs.
Does anyone know of any testing that answers the above questions or even indicates that long distance and/or high RPMs magnifies the effects of defects? i would really like to see it since I have heard both stated as fact for a long time. I have tried to find where these facts are established and haven't yet.
There are several threads on the CBF and the NOE forum answering that very question(s). Considerable work has been done pushing cast bullets of .30 caliber to higher velocities by pushing the RPM Threshold above 140,000 RPM. This has been done with 10 and 12” twist barrels using the .308W and 30 XCB Cartridges. The .308W and 30 XCB cartridges with 14” twist barrels has also been used very successfully pushing the Lyman 311466 and the NOE 30 XCB bullet to 2600 fps while maintain 1 - 2 moa accuracy to 300 yards with 10 shot groups.
A couple of us have pushed the ternary alloyed bullets to 3000 - 3100 fps with some success. However with my 30x60 XCB cartridge in a 16” twist barrel I can consistently hold 1 - 2 moa through 300 yards. I recently shot a 20 shot group at 300 yards that stayed very close to 2 moa with a velocity of 2900 fps. The first five shots were in 1 moa and the first ten shots were in 1 1/2 moa. A 20 shot test string is admittedly difficult at 100 yards let along 300 yards. I am currently still experimenting to improve accuracy.
Given the fact that most “defects” in different bullets from the same casting will not be identical in shape, weight or location on the bullet the centrifugal force will act on them differently. Therefore it is impossible to say they will hit “X” distance at 600 yards from the center of the group. However, there are formulas in several ballistics books that you can compute the effect a consistent defect in your bullets would have.
However, I don't find I can cast consistent defects so I don't bother with such mental strain. I cull the defects as best I can by visual inspection (pretty much the same as joeb does with a magnifier) and by weight sorting.
LMG
Concealment is not cover.........
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John, if they really want to learn CB benchrest shooting, it is 5 ten shot groups every week. After a few months of casting and shooting they will be good to go. They just have to learn two skills; making bullets and shooting them. If they just want to plink, they can start shooting with the first bullet they cast! Ric
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Wes has said it very well, eliminating the ability to blame something other than yourself is a very good reason to shoot the best bullet your capable of producing. My opinion exactly. Gp
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John A. wrote: “The dreaded voids are indeed a vexing problem."
I've been casting with a single cavity 80 grain Eagan mold. I inspect and weigh ALL bullets and note any visual defects under each weight. The usual range of weights is .20 grains. Discarding some high and low weights (either end of the bell curve), I end up with 80 - 90 % of the bullets cast in a .10 range.
Even with defects, the weights fall in the same range as the visually good bullets. In a recent batch of 219 cast, there were 21 bullets with base defects which were in the range of 80.06 to 80.14 grains. These fell right in the range of the visually good bullets.
Nine visually good bullets were rejected for low weight.
This leads me to believe there are voids in the “visually good” bullets as well as the rejects which have their defects at the surface.
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John, About 15 years ago at a jacketed bullet bench rest match I was talking with a guy who made match grade jacketed bullets I asked him about weighing bullet. He said check weigh occasionaly. Did not say just how often. A couple of competitors were shooting his bullets and doing very well. Aggregates at .2 MOA. He also told me something that I have never heard or read about. Some electonic scales will develop a memory.
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I'm in the camp of making the best I can and shooting the best I can make. I've made a lot of jacketed bullets, you go through the whole process, and you never know what you have until they are done and shot. And if they aren't good, it's all a waste. But if you cast a bunch of bullets, then look them over, weigh them, cull what you don't like, and toss those back in the pot. You've lost nothing but some time.
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Here is the rest of the story.
I saw the box of Berger bullets with a substantial range of weights as an opportunity to get a better idea of just how damaging to accuracy variations in bullet weight really is. To get the most severe test possible I saved all of the bullets on both high and low ends of the distribution and did preliminary zeroing and crude load work up with the ones in the middle. After zeroing the rifle, I first tried a load of 12 grains of 4227 to produced MV, similar to a lot of CB velocities. This averaged 5 shot groups of approximately 0.5 moa. Since I believed that both the rifle and the bullets were capable of better accuracy, I then tried 24, 25, and 26 grains of H322, somewhat closer to the hot loads many JB benchrest shooters use. After this preliminary shooting I had 64 bullets left.
From the 64 bullets I was able to select 12 groups. Six with bullets that varied no more than 0.2 grain, (three of the six with bullets that all weighed the same scale reading.) Although the other 34 bullets had a weight range of 0.9 grains, my best efforts could only sort out 6 groups that had a range of at least 0.5 grains. A couple of groups had a greater range.
The rifle used was a 6PPC with a Kelby action, a Krieger barrel, a 2 oz. Jewell trigger, and a typical benchrest style fiberglass stock, similar to many CBA Heavy or Unrestricted class rifles but weighing under 10.5 pounds with a 36X Weaver scope. Unfortunately, my front rest’s bag was for hunting rifle stocks but by stretching it out of shape it sorta worked for the 3” flat forearm. The friend I bought the rifle from said it would only agg. .25 moa on a good day with the best loads so was building a better one.
Without going into details, I used my limited brass supply to I shoot two groups with “good” bullets and two groups with bullets that varied at least 0.5 grains on three different trips to the range using loads of 24, 25, and 26 grains of H322 on successive days. Wind flags were not used but conditions were unusually good for the high desert with winds mostly from 10 to 2 of never more than an estimated 15 mph. All were shot from 100 yards, the limit of our range.
There was no significant difference in the size of the groups with the three powder loads. On one day the good bullets shot slightly better and on the other two the bullets with the .5 grain range in weight shot slightly better. The average for the six five shot groups with uniform weight bullets was 0.33 inches. The average for the six groups with the 0.5+ grain range in weights was 0.32 “.
Draw your own conclusions or ignore as it suits.
John
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