Weight Variation Of Cast Boolits

[Johnw...ski]

I have been casting boolits for a while always from a bottom pour pot but recently started using a dipper and a Lee 20 pound pot.

The guys on this forum had convinced me that dipping for cast boolits is superior to bottom pour and it does seem to help with the big Postell style boolits I am using.

My question is weight uniformity, don't get me wrong I weigh my boolits and shoot like weight boolits with very good and sometimes excellent accuracy, but I wonder if I can get them to weigh out more consistently.

For instance I will cast 400 or so boolits and then sort them by weight in .2 grain increments and get something like the list below:

528.0 - 528.8 25 boolits
529.0 - 529.8 50 boolits
530.0 - 530.8 100 boolits
531.0 - 531.8 125 boolits
532.0 - 532.8 75 boolits
533.0 - 533.8 25 boolits

Is this a pretty normal weight variation?

Below is my usual method of casting, can improvements be made?

I will usually mix about 75 pounds of alloy in a pot that holds about 80 pounds. I flux using a cedar shingle about the size of a paint stirer mixing well and scraping the sides and bottom of the pot. The alloy is adjusted untill I can cast boolits in a test mould that give me the weight I am looking for. The alloy is cast into ingots and stamped for identification, hopefully for future use. I will then use a Lee hardness tester and find the hardness of the boolits I cast, and after about a month test hardness again. I now know how much age hardening, if any, is going to affect the alloy.

I cast from a Lee 20 pound pot that I have attached a bracket to that holds my thermometer. When the pot is up to temperature I flux as described above then dip the edge of the mould into the lead to preheat it. With an RCBS ladle that has also been preheated I begin to cast. Holding the mould sideways I bring the ladle to the sprue hole and tilt everything upright to fill the mould, wait 2 or 3 seconds and tilt it all over and remove the ladle, ending up, usually, with the sprue full of lead. After removal of the boolit from the mould I will continue to cast in this manner. I sometimes will cast until the pot is nearly empty and then refill and reflux. Sometimes I also keep the pot full by adding the cut sprues and a 1 pound ingot as needed, fluxing often. I don't notice any differance in weight or quality either way.

I realize that I am getting less than a 1% weight variation, just wondering what I can do to improve it.

Thanks,

John

[atr]

John,
I use a dipper, but I dont cast for such heavy boolits. Mine are 211 gr max....
I also flux alot more than you seem to be doing....I flux on the average of each 15 to 20 rounds.
I also find that the mold has alot to do with casting wt. consistancy. For instance my 311413 mold at 170 grains is always dead on or within 0.1 grains....but my 311284 at 210grains usually gets up to 1 grain variation.
I find that my best consistancy with the heavier boolit is achieved when I more slowly pour the metal into the mold,,,I think that a slow pour helps displace air...
atr

[mike in co]

I have been casting boolits for a while always from a bottom pour pot but recently started using a dipper and a Lee 20 pound pot.

The guys on this forum had convinced me that dipping for cast boolits is superior to bottom pour and it does seem to help with the big Postell style boolits I am using.

My question is weight uniformity, don't get me wrong I weigh my boolits and shoot like weight boolits with very good and sometimes excellent accuracy, but I wonder if I can get them to weigh out more consistently.

For instance I will cast 400 or so boolits and then sort them by weight in .2 grain increments and get something like the list below:

528.0 - 528.8 25 boolits
529.0 - 529.8 50 boolits
530.0 - 530.8 100 boolits
531.0 - 531.8 125 boolits
532.0 - 532.8 75 boolits
533.0 - 533.8 25 boolits

Is this a pretty normal weight variation?

Below is my usual method of casting, can improvements be made?

I will usually mix about 75 pounds of alloy in a pot that holds about 80 pounds. I flux using a cedar shingle about the size of a paint stirer mixing well and scraping the sides and bottom of the pot. The alloy is adjusted untill I can cast boolits in a test mould that give me the weight I am looking for. The alloy is cast into ingots and stamped for identification, hopefully for future use. I will then use a Lee hardness tester and find the hardness of the boolits I cast, and after about a month test hardness again. I now know how much age hardening, if any, is going to affect the alloy.

I cast from a Lee 20 pound pot that I have attached a bracket to that holds my thermometer. When the pot is up to temperature I flux as described above then dip the edge of the mould into the lead to preheat it. With an RCBS ladle that has also been preheated I begin to cast. Holding the mould sideways I bring the ladle to the sprue hole and tilt everything upright to fill the mould, wait 2 or 3 seconds and tilt it all over and remove the ladle, ending up, usually, with the sprue full of lead. After removal of the boolit from the mould I will continue to cast in this manner. I sometimes will cast until the pot is nearly empty and then refill and reflux. Sometimes I also keep the pot full by adding the cut sprues and a 1 pound ingot as needed, fluxing often. I don't notice any differance in weight or quality either way.

I realize that I am getting less than a 1% weight variation, just wondering what I can do to improve it.

Thanks,

John

sierra uses plus or minus .3 for most of thier bullets.....this is machine made match.
most custom benchrest bullets are plus or minus.1 or less.
now in our world, with the size of yours i'd think 1 percent is ok. consider casting from the big pot. if you can maintain an even temp i think you will see consistancy in the mold.

mike in co

[454PB]

In my experience, weighing every boolit is a huge waste of time, and can actually make things worse. If you see a difference in grouping and chase weight variation, you're spending time and effort on the wrong problem.

I went through the same drill, segregating boolits by weight, and found absolutley no difference in boolit placement on the target or group size. I good visual inspection is all I use now.

[carpetman]

why dont you just weigh the whole batch and then divide by number of bullets?

[felix]

Air holes are the culprit. Where they are within one boolit is the unknown, and that causes the havoc. Now, this becomes more significant as the diameter of the boolit gets smaller. Why? Because an air hole is statistically the same size no matter the diameter of the boolit. ... felix

[Kraschenbirn]

John...

Without running a full statistical analysis, it looks like your max variance is within 1/2% with a standard deviation inside a 1/4%...which ain't, at all, too shabby.

I don't cast anything that heavy but a random sampling of my 400-grainers (Lyman 457124) yields pretty much the same distribution as you've recorded with approx. 75% falling within a 2-grain spread (within +/- 1 grain from numerical average).

Btw...are you casting from a multiple-cavity mould? I've found as much as 1/2% variance between cavities not be be uncommon. If you are using a multi-cavity, try keeping the boolits from each cavity separate and sorting those by weight. You'll probably find your variance reduced considerably.

Bill

[sqlbullet]

I concur with felix. Larger bullets will have a lower standard deviation in weight becuase the size of the air pockets remains reasonably constant.

As far as your bullets above, I ran some statistical analysis on them. I had to fabricate the individual data using a random number, so within each category the weights I used are evenly distributed. This would not be true with the real data.

Even so, the standard deviation for you sample came in at 1.29 grains. This is a deviation of .24% of total bullet weight. I am sure the guys casting for small bullets (say 100 gr) would be thrilled with a deviation of only .24 grains.

[BABore]

Control or keep your mold temperature consistent to reduce variation in diameter. Then sort out the light boolits to reduce ones with voids.

If the mold temp. varies, it will produce slightly different diameters and thus weights. You can't sort out the light ones (voids) with any diameter variation going on. Time your casting cadence and use a small fan to cool the open mold after dumping. Too many get hung up on alloy temperature and ignore the mold.

[jdgabbard]

The numbers look good to me. It wouldn't bother me one bit to shuffle them up and start loading. Thats pretty much what I do, and if I have any problems I look at other things. For example, I weigh handgun boolits. If I get more then +/- 5 grain variation in standard weight, I chunk the boolit back into the pot for later remelting. Just to make sure I don't get one that has too many voids. But thats just because I am super anal about a standardized weight. It doesn't affect it enough to matter. Unless your planning on competing in a 1000m match. Then it probably would.

[joeb33050]

I don't know if a bottom pour or ladle method gives the better bullet weight uniformity.
Based on my records of 19123 bullets cast and weighed, the standard deviation of weight is .151 grains, meaning that 99.45% of the bullets cast will weigh the average +/- .453 grains-or more clearly, bullets weighed +/- half a grain.
I weigh them all.
I inspect and reject any bullets with visual defects, then weigh them. Any that weigh over half a grain from the average are put aside for foulers. Then they are put into two categories. For instance, yesterday I cast some 314299s. From the cacity with a DOT, means the cavity that has a dimple put in the cavity with a punch so the dot shows, there were
202.3 1
202.4 4
202.5 3
202.6 20
202.7 49
202.8 36
202.9 4
203.0 2

Since I shoot sets of 25; 5 five shot groups, I put the 20 + 49 + 36 = 105 into a "record shooter" category, and the 1,4,3,4,2 bullets into "fouler" categories.
I do not know, nor do I think, that these "foulers" shoot worse than the "record shooters".
I think I know that the visual rejects, and the bullets, rare but now and then, that are more than half a grain from the average, shoot "off" sometimes.
I only shoot experiments, from the bench, every time.
I think I see that standard deviation is independent of average weight, that both light and heavy bullest have standard deviations of about .150 grains- 22s and 30s and 45 rifle bullets.
The great advantage of weighing bullets is eliminating those that weigh a lot more or less than the average.
I believe that your reports show bullet weights that vary much more than they could, and MAYBE won't shoot as well as those with less variation.
I THINK or BELIEVE a number of things, but KNOW much fewer. I do know what happened with the last 19,000 bullets I cast.
joe b.

[klw]

Any scale I've used in the last couple decades wasn't accurate to anything less than one grain. I'm not even sure that they are accurate to within a grain. So I think the weight segregration to anything below one grain is, well, pointless.

As to which is better, a dipper or a bottom draining furnace, that is something you can prove one way or another. Take a single cavity mould, save the bullets in their as cast order and then visually inspect and weigh them. If one casting technique is better than the other you'll see it in a graph of the bullet weights, especially if visually acceptable bullets are marked in the graph. I've done this several times. The bottom draining furnace came out ahead every time I did it.

These graphs can also be used to explore how much fluxing helps. If you make this plot and note where you fluxed you can see if fluxing had any effect. Again the several time I did this I couldn't find any advantage to fluxing. I probably haven't flux in the last 20+ years.

The largest variable I've ever seen in weight variation is variations in the alloy. If you are using linotype, high quality linotype, weight variation can be almost nill, two or three grains. If you are using something that linotype-like weight variation can range over 20 plus grains.

[joeb33050]

Any scale I've used in the last couple decades wasn't accurate to anything less than one grain. I'm not even sure that they are accurate to within a grain. So I think the weight segregration to anything below one grain is, well, pointless.
Unless you meant .1 grain, I don't understand this. Another shooter suggested that scales aren't repeatable in the past, so I did the tests below.
As to which is better, a dipper or a bottom draining furnace, that is something you can prove one way or another. Take a single cavity mould, save the bullets in their as cast order and then visually inspect and weigh them. If one casting technique is better than the other you'll see it in a graph of the bullet weights, especially if visually acceptable bullets are marked in the graph. I've done this several times. The bottom draining furnace came out ahead every time I did it.

These graphs can also be used to explore how much fluxing helps. If you make this plot and note where you fluxed you can see if fluxing had any effect. Again the several time I did this I couldn't find any advantage to fluxing. I probably haven't flux in the last 20+ years.

The largest variable I've ever seen in weight variation is variations in the alloy. If you are using linotype, high quality linotype, weight variation can be almost nill, two or three grains. If you are using something that linotype-like weight variation can range over 20 plus grains.

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6.4 RELOADING SCALE ACCURACY
On 9/10/07 I tested my RCBS 10-10 scale, using three bullets and five other pieces of lead alloy, for a total of eight test pieces.
The procedure was to weigh each test piece once, then re-zero the scale.
I weighed the set of pieces a total of ten times.
I weighed each set five times, did some errands, weighed each set three times, more errands, finally weighed each set two times.
The scale was then re-zeroed ten times.
The test pieces weighing 183.3 grains and 39.0 grains weighed the same for each of the ten tests.
Here are the weights of the other six test pieces, all in grains:
257.5, 257.5, 257.4, 257.4, 257.4, 257.4, 257.4, 257.4, 257.4, 257.4
436.9, 436.8, 436.9, 436.9, 436.9, 437.0, 437.0, 437.0, 436.9, 436.9
154.2, 154.2, 154.2, 154.2, 154.2, 154.2, 154.2, 154.2, 154.2, 154.1
159.6, 159.6, 159.6, 159.6, 159.6, 159.6, 159.6, 159.5, 159.5, 159.6
188.2, 188.2, 188.2, 188.1, 188.1,188.2, 188.1, 188.1, 188.1, 188.1
74.0, 74.0, 74.0, 74.0, 73.9, 73.9, 73.9, 73.9, 73.9, 73.9

Here are some observations:
I pull the beam, at the pivot point, toward me as each test piece is weighed. If the beam is at some place other than toward the operator, weight variations can occur. This means that if I do not pull the beam toward me, taking up the slack fore and aft in the pivot point, sometimes a different weight for a given test piece will be seen. This has been true and my practice for many years with this scale.
The location on the pan of heavier and bigger-in-area test pieces can vary the indicated weight of the test piece by half of a tenth of a grain. A 45 caliber bullet and a long sprue showed this variation.
During any test or weighing of a series of items, the pointer should approach zero from the same direction each time. From below is the direction when I'm dribbling powder. Approaching zero from up or down, randomly, can give false readings.
Frequently the beam pointer ends up pointing almost at zero. At one weight it is high, reduce the setting by .1 grain and it is low. This because the sensitivity of the scale is greater than .1 grain. This means that sometimes, frequently, the operator must decide on the closest reading.
The scale is most accurately used when the pointer scale is at eye level; otherwise the zero depends on the relative height of the operators eye. This is an uncomfortable height for me to operate a scale at, and the error is very small, less than half a tenth of a grain; so I use the scale on a table top, well below eye level.
In all cases except one reading, (436.8), all the ten weights recorded were within a .1 grain range. Either, for example, 257.4 or 257.5. Without a lot of explanation, this is a variation of +/- .05 grain.
This test did not measure the ability of the scale to weigh a known weight and zero at that known weight. Means that no known weight of, for example, 50.0 grains was weighed and found to zero at or weigh 50.0 grains. This test did measure the ability of the scale, (and operator), to zero at the same weight repeatedly for ten tries.
As long as one starts low on the powder charge, then works up, there is no problem with a scale that repeatedly reads (slightly) "off".
Accuracy is about at least three things,
"does it read WW.W when I put a known WW.W weight in the pan?"
"does it do that across the range, from, say, .5 grains to 500 grains?"
"does it repeat readings, across the range"
All I did was the third. The reason has to do with my experience that all scales I've checked against each other were very close, differences about tenths of a grain. Also, because there's nothing one can do with a beam balance if it reads "off", other than constructing an unusable correction chart or throwing the thing out.
If a scale zeros at 49.0 grains with a 50.0 grain weight traceable to NIST, all you can do is throw it out. A scale/beam balance can't be calibrated, no more than a 6" ruler or a 0-1" micrometer caliper.
And, I've never even heard of a scale out by a grain.
So, that's my thinking.

The RCBS 10-10 scale can be adjusted in 10 grain increments in two ways.
First, we can put the left hand big weight at 10 or 20 or 30 or ........., and keep the right hand rotating cylinder thing at zero.
Second, we can set the left hand big weight at zero and the right hand thing at 10 = 10 grains, or the left hand weight at 10 and the right hand thing at 10 = 20 grains, or the left hand weight at 20 and the right hand thing at 10 = 30 grains, or.........
A poster on Cast Boolits reported that his scale read different weights with the two ways of setting the scale.
On 9/23/07 I cranked up the 10-10 scale to see if it did the same. First using the left hand 10s and right hand 1s weights; then using only the 10s weight. Here are the results:
10 = 10
20 = 20
30 = 30.1
40 = 40.1
60 = 60.1
80 = 80
100 = 100
This test took a while, a lot of zeroing was going on, and adjustments, and deciding about less than tenth grain differences. As shown, this is as close as I could call the readings, but in every case there was a difference of less than a tenth of a grain- the X0-X0.1 readings were closer to .1 grain than to .0 grain.

joe brennan

[Johnw...ski]

Thanks for some really great replies.

I weigh all my boolits to weed out extreme weight variations and I agree that segregating them into .2 increments is not necessary but since I am weighing them anyway that is what I do. I have shot groups with boolits whose weight was held to within 1.0 grain and they show little if any increase in group size, at least at 100 and 200 yards. I often shoot casual matches with friends where the loser buys lunch. The match consists of 15 shots offhand at 100, 200 and 300 yards using the standard military target for each range. I hate to pay for lunch so I try to put in the extra effort into my reloads.

From the replies I have gotten it seems I am not doing too badly overall and any improvement will be from more careful attention to the temperature of my mould.

Thanks again for the help with quality controll.

John