Weighing bullets-statisically speaking

[MIEagle]

Will randomly selecting 10 bullets out of, say, 50 or 100 in a casting session, to weigh, add up and divide by 10 to give me an average weight be valid to then separate by + or - by 0.5 grains? I don't want to make more work for myself than I need to but I want to do it right. These bullets are used for BPCR silhouette shooting. Thanks.

[NSB]

Not exactly "statistical". An average doesn't mean much. The average of zero and a hundred if fifty. The average of forty-nine and fifty-one is fifty. Which one has the most variation? If you're not familiar with stastical methodologies, the simplest thing to do is throw out the top third and bottom third of your weights and average the remaining for "average". The ones too far out either way will be your biggest cause of variation. This isn't an exact way to describe a statistical method but it's close enough. Remember, Mark Twain once said, "if a man were standing with one foot in a bucket of ice water and the other food in a bucket of boiling water, on average he'd be quite comfortable". Don't put much emphasis on averages. The more parts you weigh, the better your "average" will be. I'd do at least fifty if I had them and the time to do it. FWIW, if it were actually me I wouldn't do any of it. I'd pick the number that's the most common weight and for a very heavy bullet I'd go +/- 1.0g and for lighter bullets I might go =/- .3g. That's not very scientific either but experience tells me I'd be in pretty good shape for shooting.

[Don McDowell]

Better off to weigh each and separate throw out anything that goes beyond a 1.5 -2 gr spread from the "zero" mark. Then you could sort and group down from there, but if you've done a good job casting a 1 gr or less spread will be the norm and not much need to sort down closer after the initial weigh in.

[country gent]

wiegh a session out each and see wha the curve in wieght actually is with a given mould alloy. Ill et its alot steeper and narrower than you think it is. A piece of poaster poard divided into 3" sections with a magic marker works good for this when done look at the "peak" then ad in +1grn and -1grn see how many of them fall into that range

[Lead pot]

I'm going to say this with all due respect.
If your getting a bullet during your casting session after the mould gets up to temperature that weighs less then 5 or as much as 6/10 gr below the heaviest your not casting very consistently.

[MIEagle]

I'm working on refining my casting technique. I weigh my lead and tin to get a 30/1 mix. I use a propane stove, 1 1/2 qt iron pot and the dipper method. I have a Tru-Tel thermometer and try to cast at 750 degrees. I regularly flux, stir the pot before dipping and clear off all dross. I hold the meld on the mold for at least 8 seconds. I drop the excess sprues in a separate coffee can. I try to be consistent in rhythm casting. Today I used the Lyman .457125 mold casting. Of 60 bullets cast, the temp was between 700-750 degrees, the average was 519.6, the top cut off was 520.1 and the bottom was 519.1. I had 34 bullets between 520.1 and 519.1. There was 11 bullets above 520.1 and 15 below 519.1. The gas control on the regulator hose is not real exact so I have to watch for temp swings. These bullets were closer to the 700 degree temp. Your thoughts? I appreciate it. Thank you.

[Jim2]

I use certified alloys and on a good day my bullets are in a spread of 3/10 for a hundred cast during the same time period, without adding any alloy to the pot. Molds used are either BACO or Brooks. Paying attention to details will provide you with a good bullet, all things being equal .

[Don McDowell]

It's a hard thing to do, but the first 8-10 bullets you pour should go right into the sprue bucket. I'ld say for the most part you're doing alright, but as you have already figured out the temperature swing is getting several culls. Might want to consider one of the Lee solid bottom pots, they do hold temp fairly well after you get the melt to temp.

[country gent]

Pour as large a sprue as possible, keep the base molten long enough to fill and off gas the mould.Also what ladle are you using? Lees are at the bottom of useable. Lyman and rcbs are good and may benifit having the spout hole opened up to .200 - .210 dia to fill faster. Are you pouring or pressure filling? Try both also when pouring try both a center pour right thru the sprue hole and also a "swirl" along the edge of the sprue hole chamfer. Wach the first few bullets when cast for visible defects discard first 8-10 drops as general practice "just in case". Always start with a full ladle. "spill a little out and onto sprue plate at first, then fill mould letting a little over run the spru and spill back into pot. Where at in michigan are you if you dont mind me asking?

[Idaho Sharpshooter]

I read a book written by some gentleman named Pope. He made bullet blocks, held 60 (iirc) bullets each. He would cast and throw the first dozen or so back, then start keeping them. Drop a bullet out of the blocks, pour another, and set the mold down. He then picked the bullets up with tweezers and inspected the base. If it looked good, it went in the hole. When a block was full, he put more alloy in, fluxed, and repeated the cycle. He said that he could cast, using a 215-220gr bullet design, and hold a .5+/-gr spread on 240 bullets. He lubed and stored, and shot them in order cast. As I read, he did rather well with that method. Anything outside that spread were used as foulers/sighters.

I found that the first dozen cast would very slightly increase in size (.0005 to .001gr) and weight (2 to 2.5gr) as you cast, before settling down to keepers.

Rich

[JSnover]

...average was 519.6, the top cut off was 520.1 and the bottom was 519.1. I had 34 bullets between 520.1 and 519.1. There was 11 bullets above 520.1 and 15 below 519.1.

+/- .5 gr. on a 520 gr. mold is pretty tight, just a smudge under two tenths of 1%. If Pope was satisfied with +/- .5gr in boolits that only weighed half as much, I'd say you're doing pretty well.
Put another way, your boolits that are within half a grain are 99.8% perfect.

[MIEagle]

I cast out in the old cow barn and fire up the generator to run the lights. My stove is a single burner Chi-com cast iron frame camp stove run off a 30# propane tank. The gas control is so sensitive that to increase/decrease heat I have to watch the flame intensity and wait for the thermometer to respond. I use the Lyman and RCBS ladles. I stir the pot, fill the ladle and pour some off so it won't spill all over the mold. I tip the mold to the ladle and fit the ladle and mold together, holding for 8 seconds, then separate the two and try to get enough lead on the sprue plate to form a nice sprue. I wait about 5 seconds after the sprue hardens and drop them out in order cast. Lately, I have been numbering them with a black marker to keep track of them. I weigh them, separate them into 3 groups. The ones that are too heavy or too light, I discard or use for fouling shots. I live in the northern Lansing area and shoot at the AP Goodrich range located between Ithaca and Alma. Thanks for your suggestions.

[rfd]

casting good bullets is an art form of sorts. there are many variables and pitfalls to consider. if yer not dropping bullets with more than a 2 grain variance, something ain't right. and when it all comes together, the variance should be 1 grain at most. besides the temperature factor of alloy and mould, how tight the mould handles are held will have a direct effect on the dropped bullet weight. with locking mould handles, if i do my part i'll get a .5 grain or less variance. another factor is the sprue plate - too tight and the bullet base will have rounded edges - you want the plate a tad loose to allow air to escape and give you that crisp, sharp bullet base edge.

[Lead pot]

I don't mean to sound harsh when I say your not casting very consistently.
I cast with a very tight sprue plate and my bullets have a very sharp flat base. My plate is so tight I have to push it with a wood dowel and I do not have a rounded base problem. Most of the variances come from a loose plate lifting up and letting more lead accumulate above the block. It does not take much to gain a couple 10's of weight. Start your pour with the plate on it's side. This will fill most of the mould then slowly turn the mould up holding the spigot of the ladle tight on the plate for a couple seconds then raise the ladle while the rest of the lead is still pouring out over the sprue hole. The vibration of the lead hitting the top of the hole will settle the lead in the cavity, kinda like a vibrator will settle concrete in a form or powder in a case. Also this will eliminate the gray smudge you see on one side of your cast bullet that looks like a blemish.
Lite bullets are also caused by the dross sticking to the ladle spigot. when you hear some saying "voids" in the bullets, well if you split one of those very lite bullets you will more then not find dross in that bullet that got poured through the sprue plate. To keep this from happening take a rag that has some lube on it from wiping up spilled lube or touch the hot ladle on a block of canning wax and wipe it off. this will keep the dross from sticking on the ladle spigot so it don't end up in the mould.
Just following little things I just mentioned will give you very close bullet weights. I don't weigh any of my bullets anymore. I can tell when I have a bullet that will be light by just looking at the sprue puddle how deep the dimple is when it hardens. My variances run most zero +- and seldom more then 4/10's from light to heavy. And it don't matter if I cast soft 1/40 or hard 1/16 and I cast from 700 to 750. Depending on the tin/lead content. The more tin the less the temp.
Kurt

[wills]

I saw this several years ago.

This was originallyposted by HP guy in the BPCR group at MSN
“Cast 100 Match GradeBullets Per Hour”

Good evening,

Much has been written about bullet casting technique. Butafter 5 years of serious casting the information gleaned from books andarticles read have not filled the gaps to allow production of 100 match gradebullets per hour. For the purposes of this post, match grade refers to castbullets with perfect base edges, no base divots in the middle, no surfaceimperfections (surface wrinkles, frosted bullets, slag on surface, lack ofgroove definition, etc.) and weight range from first bullet to last of about1/2 grain. That sounds like a tall order, but if we only aim low we just mighthit our feet.

Fifty bullet casting session have been the norm of late. Thesessions last about 28 minutes. The last casing session stats are as follows:

30 minutes

54 bullets with no bullets returned to pot

First bullet weight = 403.5

Last bullet weight = 403.6

Max bullet weight = 403.6

Min bullet weight = 403.1

The only way to insure that the first bullet out of the moldis a match grade bullet is to pre-heat the mold. The current method is perfect.The scientific hot plate that is used for the dip-lubing process is also usedto pre-heat the mold. This hot plate works better than the stove burner becausethe heating surface is flat and solid. There are no coils so the completebottom surface of the mold is in contact with the heating surface. After alittle experimentation to determine the heat setting, 8.5, the first bullet outof the mold is in the match grade weight range. The bottom of the mold must becompletely free of lead speckles, as must the mold faces.

To determine which setting on the hot plate to use anestimate was used to start, 6.0. The first bullet out had a surface wrinkle onthe ogive indicating that the mold was not hot enough. Next 7.0 was tested,still slight ogive wrinkle. Next 7.5 was tested with no wrinkles. After casting50 bullets they were weighted in order cast. The first 4 or 5 bullets wereunder the 1/2 grain match grade range which means the mold is still a bit toocool to drop a match grade bullet with the initial mold fill. Next the 8.5setting was testing. All bullets from first to last were within the 1/2 grainmatch grade range. If the setting is too high and the mold too hot the bulletswill be frosted and even if they are not the first few will weigh more than the1/2 grain match grade range. Frosted bullets are not optimum for silhouette asthey are more frangible than properly cast bullets.

I’ve included a picture of the current mold heating setupfor your review. This dandy scientific hot plate can be purchased from:

http://www.storesonline.com/site/251298/page/31550

The model is:

Thermolyne* student hot plate, 120v, 50/60hz, 2.7a, 325w(UL)
Item No. HP2305B EA

The hot platecurrently does double duty as mold pre-heater and dip-lube process tool.

Based on much experimentation, the most important variableto control is mold temperature to accomplish the 100 match grade bullets perhour goal. It is mold temperature control that will help you the most inachieving a very narrow range of bullet weights.

Next, for high output volume per unit time the mostimportant issue is a quick and consistent casting technique. More on thatlater.

One area that has been often neglected in texts read is melttemperature. Most casters are using too high of a temperature. The lowesttemperature that will give excellent mold cavity fill is best from an outputper unit time standpoint. The cooler the melt, the faster the spru can be cut.The bullet mold used the past week casts a 404 grain, 1.50" long38-caliber bullet with no grease grooves. The melt temperature is only 750 F.The spru is ready to cut in about 3 seconds from the time the ladle is rolledoff the spru hole.

It is technique like the above that will help to increaseone’s bullet casting output and improve bullet quality.

All the best,

Dan Theodore

[EDG]

Statistically speaking you will need a digital scale that is very dependable and accurate - many of the cheapos are not.

Next you have to weigh a statistically valid number of bullets. That is at least 30.

With a digital scale you might as well weigh all of the bullets. Record the weight of each.

Using Excel or similar program create bin sizes that you think appropriate .1 gr, .2 gr. .5 gn or maybe 1.0 gn. After you play around with the bin sizes a little you will recognize what size will make sense. Then count out the number of bullets in each bin and graph the results.

You will see a bell curve with light bullets that did not fill out or contain gas inclusion on the left of the curve.

In the center you will see most of the bullet weights.

The right side of the graph will contain the heaviest bullets but the right hand tail should be cut off.
It should be cut off because the mold has a finite limit of alloy volume that it can hold. Anything heavier than that volume can only be caused by poor technique such as the mold not being completely closed or different alloy with a higher percentage of lead. The right tail has a maximum weight assuming you get the mold closed and never vary the alloy.
The lighter left hand tail has no limit since short pours can go all the way down to zero.

If you can get 30 or 40 of the heavier bullets in a narrow weight group shoot them. All things being equal meaning they fit your barrel properly they should be the most accurate bullets.

However do not look at this as work. Look at it as learning.
You are accurizing your ammo by gaining more knowledge.

If you do not want to mess with Excel or graphing send me the weight data and I can graph them for you.

PS an average is like having one hand under the hot water faucet and one hand in a bucket of ice water.
By the average temperature you are comfortable.

What you might prefer is the standard deviation - which is a number that that describes the variability of the entire lot.

[MIEagle]

Thanks to all. Some of the advice I'm already doing. Some that I have not, I will do. During the last casting session, the sprue plate, the heavier replacement plate, on the second hand Lyman .457125, became loose on the pivot screw but I kept going as I only needed 30 to test out some charges. I will fix it. My casting ladles get cruddy from oxidation so before casting I scrape off as much of it as I can, inside and out. I made a "bore punch" out of a 3" course threat drywall screw, cutting the head off and affixing a handle, to scrub out the spigot. I could probably buy a new one. I will pay attention to the crud in the spigot. My digital scale is a $30.00 MTM scale. I will up grade when I can afford it. Two casting sessions ago, I cast 100 Steve Brooks bullets, Creedmoor, I think (second hand mold) and numbered each as cast. I weighed all of them, then set up a graph with the bullet # on the X axis and the bullet weight in 0.1s on the Y. Although most of the bullets were within the + or - .5 spread, there were some extreme spikes caused by my being distracted by something, not immediately closing the mold after knocking the bullet out and arranging it in sequence. I will be more critical of what I do. Thanks!

[John Boy]

Read the article and then tack the chart on the wall where you cast -
The 8-Phase Casting Cycle ...http://www.longrangebpcr.com/8Phases.htm

[Ballistics in Scotland]

I'd agree that it isn't really the average that matter most. For many purposes a fraction of a grain over or under is neither here nor there. What matters far more is a cavity inside the bullet - no more than a rounded base, especially one that isn't equally round, all round. But you can see a failure to fill the edge at the base. You can't see a cavity, or whether it is off centre.

If you have an electronic scale that has a tare facility, you can weigh a few consistent bullets, and set zero at that level. When you get a bullet appreciably underweight, discard it.

[Gunlaker]

MiEagle, I spray my ladles, and the exposed areas of the pot ( after they've cooled) with WD-40 to help reduce oxidization. Anything you can do to ensure the alloy is clean and dross free is a good thing.

Also one of the best things I've done for casting good bullets ( in addition to not using a bottom pour pot which I di for several years ), was to use a hotplate to preheat the mold. The first several bullets still come out light, but they are almost always well formed. I can get good bullets after tossing back maybe 5 or 6 before the mold is 100% up to temperature.

Chris.