Why weigh bullets?

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CB posted this 21 June 2007

(this thing is getting too messy, I can't find things. I'm going to start new topics as needed.)

Why I weigh cast bullets.

 

A. Weighing allows me to eliminate “strangers". My average lot size over some 14620 cast bullets weighed and recorded is 107. This does not include the “strangers", those bullets that weigh more than a half a grain away from the mean. I generally find 1-3 of these. I assume that these strangers will shoot less accurately.

B. Weighing allows me to segregate or class bullets. I shoot sets of 25 shots, every set is an experiment. I need sets of 25 bullets plus 1-2 in case I drop one. After weighing it is easy to select these sets of bullets with little or no weight variation within each set.

C. Weighing allows me to understand better what is going on during casting. For example, I had suspected trouble with a lot of 25:1 that I bought, and had been casting with a mixture of lead and a little foundry type. After each lot I added lead to the pot, wanting softer bullets. Each lot had the average weight increase. This lot has an average of 183.6 grains, and a standard deviation of .171 grains.(183.3-184.0 only.) There's not enough ?tin?, certainly not enough something, because the quality of the bullets has gone down based on the variation and the appearance. There are many other lessons I've learned by weighing bullets.

D. Weighing allowed me to calculate and record the average weight and standard deviation of weight of each lot of bullets cast; and this data leads me to this conclusion: After eliminating “strangers", the standard deviation of bullet weights, on average, for >14000 bullets, is .151 grains-and this includes some very messy results. Then it is reasonable to say that under proper conditions a caster should be able to cast bullets that weigh +/-.5 grains virtually every time, and with culling, lots of bullets can be held to +/- .3 grains easily. ( I suspect that variation is not a function of average bullet weight, but don't know, yet.)

 

Does weighing cast bullets matter?

Based on the results of the testing performed with round-filed bullets in 2007, it appears that pretty big holes or bubbles in cast bullets have a pretty small effect on accuracy.

In the arena where average five shot group size at 100 yards is 2” or greater, weighing bullets may not matter.

Where average five shot group size at 100 yards is <2", it MAY be true that careful inspection, weighing, culling and segregation substantially reduce group size.

It has often been stated that with average group sizes well under 1", that weight variation within the feasible range increases group size substantially. However, data to support this belief is sorely lacking, and needed.

 

Why does cast bullet weight vary?

This is what I think, not what I know.

Bullet weights from the same pot of alloy vary, at least mine do, even after visual inspection and culling under a 4X lighted magnifier.

I think that there are only a few causes of this weight variation.

First is holes or bubbles in the bullet, not visible during inspection.

Second is “incomplete fill out” or rounding of some edges, slight enough to be missed during inspection.

Third is due to variation in weight due to variation in diameter/shape due to variation of the pressure with which the mold is held closed.

I think that weight variation due to alloy composition is ruled out because of the “same pot of alloy” condition.

joe brennan

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PETE posted this 21 June 2007

 Joe,

Third is due to variation in weight due to variation in diameter/shape due to variation of the pressure with which the mold is held closed.  You can also add variaition in pot & mould temp. will affect bullet wgt. All the pots I've used over the years start out varying about 10 degrees from lite on to lite off. As they age this increases to about 20 degrees when it seem to stabilize. I don't know of anything you can do to correct this either.

  Then mould temp. has been shown to affect the wgt. I'm sure we've all noticed that bullets tend to get heavier toward the end of a run. Some tests have been run with thermo-couples attached to moulds and the mould allowed to vary in temp. and the wgt. of the bullets recorded. This mould temp. seems to be the critical factor in bullets varying in wgt. The closer you can keep the temp. the closer your wgt. variation will be.

  Added onto to your reasons it does seem a wonder that we can cast anything like close wgt. bullets. Sometimes some of my casting sessions would make you think I had all the above problems at the same time! :)

I think that weight variation due to alloy composition is ruled out because of the “same pot of alloy” condition.   I agree and it's why I keep all bullets from the same pot of alloy separate.

PETE

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CB posted this 25 June 2007

Joe Brennan wrote: Does weighing cast bullets matter?

It has often been stated that with average group sizes well under 1", that weight variation within the feasible range increases group size substantially. However, data to support this belief is sorely lacking, and needed.   

Bottom line is what shows up on the target. My experience has shown me that segregating bullets from a two cavity mould helps, indexing bullets by placing a small mark on the ogive helps, using wind flags helps (big time). Weighing to +/- a tenth grain in a normal casting session doesn't seem to make much of a difference.

To me this is a lot like weighing vs dumping powder charges. Weighing hasn't been proven to improve accuracy while it seems that it should. If someone can prove that weighing made a substantial difference I'm all ears but up to this point what's been said and proven to the shooters that did the comparison is that it doesn't.

I don't think I have the casting skills to drop bullets with intentional voids or 1 1/2 grain weight variations so maybe weighing would help in those cases. I don't start saving bullets until the mould and pot are up to temp. and throw back bullets where the base isn't filled out so maybe that why I don't see any difference between “match grade bullets” and foulers.

Or maybe I just don't set the bar as high. 

Pat

 

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PETE posted this 25 June 2007

 Pat,

Weighing to +/- a tenth grain in a normal casting session doesn't seem to make much of a difference.   I think you're probably right and a looser spread might work just as well. But I don't know how much that would be so it makes me happy to keep it as tight as I can! :)

  It would be an interesting test, if it was possible to do it, to see, say for a .30 cal., how much variation it actually takes to get a noticeable difference in accuracy. I don't know. So I weigh all my bullets.

  For your own use what would you consider to be an acceptable spread?

  The one thing I've found in casting over the years is that every session will have several bullets that will weigh .5 gr. + or-, or more, from the norm. Sometimes if the phase of the moon isn't quite right they'll be a full gr. off. They can even be heavy, which does tend to confuse me. The ones that go light I assume have a void in them.

  With the electronic scales we have these days I like to get rid of these “weird” bullets.

PETE

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CB posted this 25 June 2007

Pete,

Most of my casting is with one cavity  moulds and if I use a two cavity the bullets are segregated. Once the mould and pot are up to temp and throwing good bullets weighing a batch will show 6 or 7 tenths difference on average with the majority within +/-  2 tenths of mean. I wouldn't know how to cast a batch of bullets with enough weight variation to be able to find out how much would be necessary to show on the target but I don't think a half grain does .  

We could discuss this stuff til we're blue in the face and I'll continue to weigh and segregate the bullets I shoot in matches into +/- 1 tenth groups but I don't think it's gaining me anything except peace of mind.

This seems like such an easy thing to test for oneself that further hypothetical discussion on it seems useless.  I don't think one person who's replied to the weighing bullets threads has said they were able to prove to themselves weighing showed up on the target.

Pat

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CB posted this 25 June 2007

I agree with Pat. I use 2 cavity moulds for my match stuff and I do weigh them in 1 tenth groups, mainly for peace of mind and that is how I was taught.

Other than that I have no data that either supports or disproves that it makes a difference.

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billwnr posted this 25 June 2007

I use a 4 cavity NEI and weigh and order my bullets. I use a bump die and that negates any differences between the 4 mould cavities.

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PETE posted this 25 June 2007

 Pat,

We could discuss this stuff til we're blue in the face and I'll continue to weigh and segregate the bullets I shoot in matches into +/- 1 tenth groups but I don't think it's gaining me anything except peace of mind.   Exactly! After you've worked up a good load it becomes more a matter of confidence in yourself that counts the most. To me, at least, this is eliminating all the variables I can think of so that little gremlin doesn't sneak into my mind questioning whether that bad shot was one of those things I didn't take care of.

  Here's one for you to think about. :) I got to thinking one time if maybe a guy ought to face in a certain direction in relation to the range he'll be shooting on at the next match. Got to wondering if the molecular alignment as the bullet hardened would make a difference in accuracy. But, since I face north when casting and all the ranges I shoot matches at you face north I never got around to experimenting with that idea. But maybe I ought to face another direction. Maybe Joe has an opinion on this! :)

This seems like such an easy thing to test for oneself that further hypothetical discussion on it seems useless. I don't think one person who's replied to the weighing bullets threads has said they were able to prove to themselves weighing showed up on the target.   I'm not to sure this would be as easy to prove as it might sound. Casting out of wgt. bullets would be easy, or you could file some off the nose. The difference would probably be so small until you got to some ridiculous variation it would be obivous. But, as a target shooter I would want to know when you get a difference that could easily be covered up by some other condition.

PETE

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CB posted this 25 June 2007

PETE wrote:   I'm not to sure this would be as easy to prove as it might sound. Casting out of wgt. bullets would be easy, or you could file some off the nose. The difference would probably be so small until you got to some ridiculous variation it would be obivous. But, as a target shooter I would want to know when you get a difference that could easily be covered up by some other condition.

PETE

Pete,

What you wrote above is exactly the point, it'd be pretty hard to cast some ridiculously out of weight bullets. Next time out just don't weigh a batch of bullets and see if there's a difference on the target. Seems a pretty easy test to me.

We don't normally file our bullets so while it's interesting for conversation's sake it doesn't apply to the real world. If you can cast .30 or .32 cal bullets on demand for testing purposes that vary 1 1/2 or 2 grains you're a better man than me. Bottom line is that during normal casting sessions where you're getting good looking bullets I don't think you'll be able to see a difference on the target. The problem lies in the fact that we all tend to tell new shooters that it's an absolute necessity for extreme accuracy without ever putting it to the test.

Pat

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JeffinNZ posted this 25 June 2007

I recently did my 'annual' run of round balls for my .40cal muzzleloaders.  After weighing about 40 of the balls and finding them consistant to the point of being BORING I demonstrated enormous self restraint and refrained from further weighing instead visually inspecting only.

Took a fair amount of self control not to weigh each one though.

Who's a creature of habit?

Cheers from New Zealand

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CB posted this 26 June 2007

pat i. wrote:

Pete,

We don't normally file our bullets so while it's interesting for conversation's sake it doesn't apply to the real world. Pat

Since none of us can cast lots of bullets that weigh substantially less than average, and if we want to find out if weight variation affects accuracy, one method is to file some weight off the outside of the bullet-simulating a “hole", and test those bullets for inaccuracy.

That's why and what I did, as has been explained several times here.

It remains for one of the smaller group shooters to file a bit off some bullets and test to see how accuracy changes, or to devise and perform another test.

A test of 5 groups of 5 shots at 100 yards with a very accurate rifle, in the course of other testing, would be very valuable.

Why doesn't one of you do such a test?

Tomorrow I'll test the .1 grain files 22 RF bullets.

joe brennan 

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CB posted this 26 June 2007

PETE wrote:   I'm not to sure this would be as easy to prove as it might sound. Casting out of wgt. bullets would be easy, or you could file some off the nose. The difference would probably be so small until you got to some ridiculous variation it would be obivous. But, as a target shooter I would want to know when you get a difference that could easily be covered up by some other condition.

PETE

Pete,

You are so right about other conditions having more of an influence. Those other forces are greater than the force of cast bullet's weight variance, though weight variance is a differential force of it's own.

Segregation of weighed bullets is not so called conventional wisdom, theory, opinion, or old wives's tail, it is sound mechanical design. No one builds a match rifle saying .001” or .002” to center is mechanically close enough, but to achieve symmetrical design as absolutely close to exact as possible. As close to exact as possible cast bullets is a sound mechanical criteria and weight is a good indicator toward a band not filled out completely, or somewhere on the bullet, that can't be measured. Weighed bullets is a constant, not just a self confidence factor..............Dan W.

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CB posted this 26 June 2007

Joe,

What more testing do you want me to do than actually compare weighed vs unweighed bullets that I cast in my guns. I don't normally take a file to my bullets or cast bullets with a 2 grain spread so both things don't pertain to my shooting. For conversation they're interesting experiments but since trying to get my new barrel to shoot is a little more important than performing tests for testings sake alone that don't apply to me I'm not inclined to waste time, energy, powder, and lead on something that I've already proven to myself doesn't make a difference.

Dan,

Mechanically weighing bullets makes perfect sense, as does weighing powder charges, getting the ES as close to zero as possible, using only powders that fills the case to the bullet base, and plenty of other things that in theory should lead to better accuracy but in real life experience haven't been shown to pan out. I truly believe most if not all people would find that if they left their opinions out of it and ran unbiased side by side testing they wouldn't find any difference in weighed vs unweighed bullets on the target. 

I'm also going to include something I wrote in another thread for your opinion since it wasn't really addressed where it was.

"Let's say you weight segregate bullets into two groups, 1 batch 200 grains and the other 199.5 grains, what's to say half of the 199.5 gr. group aren't in reality 200 gr. bullets with a 1/2 grain void? Weight segregating makes perfect sense from a logical stand point but is it really helping?"

Like I've been saying all along but getting no where with is that guys who actually shot the w vs uw bullets side by side agree they can't tell the difference, the rest are just going by what seems like a logical conclusion and stating it as fact.

Pat

 

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CB posted this 26 June 2007

PETE wrote:  Joe,

 You can also add variaition in pot & mould temp. will affect bullet wgt. All the pots I've used over the years start out varying about 10 degrees from lite on to lite off. As they age this increases to about 20 degrees when it seem to stabilize. I don't know of anything you can do to correct this either.

  Then mould temp. has been shown to affect the wgt. I'm sure we've all noticed that bullets tend to get heavier toward the end of a run. Some tests have been run with thermo-couples attached to moulds and the mould allowed to vary in temp. and the wgt. of the bullets recorded. This mould temp. seems to be the critical factor in bullets varying in wgt. The closer you can keep the temp. the closer your wgt. variation will be.

  Added onto to your reasons it does seem a wonder that we can cast anything like close wgt. bullets. Sometimes some of my casting sessions would make you think I had all the above problems at the same time! :)

PETE

Will changing lead pot temperatures change the weight of cast bullets?

This is an approximation.

Iron/Steel as in bullet molds has a coefficient of linear expansion in temperature of about 11 parts per million per degree C.

Volume~weight of the cast bullet varies as the cube of mold dimensional changes, hotter molds are bigger molds and cast bigger bullets.

A degree F = 5/9 of a degree C, so the coefficient is ~6.1 parts per million per degree F; cubed is ~ 228 parts per million of WEIGHT per degree F.

Or, .023 grains per 100 grains bullet weight per degree F.

So a 10 degree F change in mold temperature of a 100 grain bullet causes a .23 grain ~ quarter grain change in bullet weight. If I did this right.

So, fluctuating mold temperatures will cause significant changes in bullet weight, as Pete said.

 

joe brennan

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CB posted this 26 June 2007

I have PMC Match Rifle 22 RF bullets triangular filed with .1 grain and .3 grain filed off the sides. Here's the .1 grain bullets:

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CB posted this 26 June 2007

Here are the bullets with .3 grain filed off-.3 grain is a lot. I had to weigh each bullet before filing, then re-set the scale and file. Here's the recorded weights of 30 cartridges in grains:

51.5-1

51.6-2

51.7-3

51.8-5

51.9-4

52.0-6

52.1-4

52.2-2

52.3-1

52.4-3

The average weight is 51.9 grains and the standard deviation of cartridge weight is .228 grains. To put this in perspective, the standard deviation of cast 30 caliber bullets can be pretty easily held to .150 grains; so that .228 grains is A LOT. What do it mean?

joe brennan  

 

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PETE posted this 26 June 2007

  Dan,

  Guess I never looked at weighing bullets as being sound mechanical design, but sure do see your point. To me it seems like you have to take all the little “improvements” you can come up with and add them together to get the whole picture of what accuracy is. Each little thing you do might only subtract, say, a 1/16” from the group. But if you get a good barrel and have a good smith make you a rifle that will subtract quite a few 1/16's from your groups. Then all those little things you can do when casting helps to.

  Now there's nothing wrong with “plinking” ammo. I've shot a lot of it myself, but even at that I like to see what that plinking rifle will do with a little work.

 Joe,

So a 10 degree F change in mold temperature of a 100 grain bullet causes a .23 grain ~ quarter grain change in bullet weight. If I did this right.   In actual practice it's probably a little more than that...... depending on caliber of course. For a .30 cal. it might be something on the order of + or - .2 over a run. For the 100 grs. in your example it might be a little less, say + or - .1 gr.

  The thing we have to keep in mind is that as the mould vaires in temp. so does the pot, and off the top of my head I'd say that both will keep “time” with each other. I try to smooth out the mould temp. by casting at the rate of a little over 200 bullets an hour. You have to be very careful in how you regulate things. If you think about it as the mould heats up your casting rythmn will slow since it takes longer for the sprue to harden. So I regulate this by touching the sprue plate to a damp sponge and by having a record of the temp. the mould works best at. Usually about 800 deg.'s covers most.. You can keep a pretty close eye on the mould temp. by how your bullets drop out. If they stick then the mould is a little to hot and I leave the sprue plate on the sponge a little longer.

  Since I keep my bullets in the order cast, more so I can keep count of them, I find that the ave. wgt.s tend to rise and fall as you go along.

  Another thing you have to be aware of that seems pretty consistent is that as the pot level goes down the bullet wgt. goes up to. Not sure why this happens. Any guesses?

The average weight is 51.9 grains and the standard deviation of cartridge weight is .228 grains. To put this in perspective, the standard deviation of cast 30 caliber bullets can be pretty easily held to .150 grains; so that .228 grains is A LOT. What do it mean?   It do mean that the priming compound varies quite a bit, with the powder charge being a close 2nd. In CF primers this is the biggest factor in the differences in weight. The cup and the anvil, for all practical purposes, weigh the same. JUst to forestall yourr next question..... Did the experiment so that's facts speaking and not guesses. :)

PETE

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CB posted this 27 June 2007

On 6/27/2007, Model 12/15 BSA Martini, Lyman STS 30X, 50 yards, windy and starting to rain in fits.

Perfect, .1 grain filed, .3 grains filed ammunition.

This gun, like the rest, loves Eley Match ammunition.

I was going to file some Eley Match Red Box, I had the file in one hand and the first cartridge in the other, but a force stronger than I, (and I am enormously strong), kept me from touching that Eley cartridge with the file.

I was able to file the PMC Match Rifle, this ammunition works well in this gun.

Group sizes, leaded edge to leaded edge - .244", all in “

Perfect -.1 gr            -.3 gr.

.433     .473            .353    

.382     .564            .324

.439     1.294            .394

.419     .732            .546

.547     .443            .910

Avg.     Avg.            Avg.

.444     .699            .505

 

Here's the target

joe brennan

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tturner53 posted this 26 October 2009

Wineman loaned me a mold, a GB Lee 6 cavity .318 Loverin style going about 174 gr. Mine has averaged 174 gr., with a spread from 173 up to 174.5, and an occasional oddball. This is after visual inspection. Seems to me to be pretty good for a 6 cav. , but without weighing I'd have those oddballs in there, and I'm trying to find some target loads. You guys talk about .5 gr. increments not making a measurable difference, what about 1.5 grs.? These are for my milsurps with iron sights.

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corerf posted this 26 October 2009

tturner53,

Personally I segregate into 1 gr groups and load knowing the groups will vary. I mean, I load 221.5 to 222.5 bullets, say a lot of 10 in multiples of 5. Then as I box them, they are arranged in fives, tens, etc. So the cases are sorted after loading. As I pull, I know that my 5 shot groups will weigh the same, from group to group there might be a substantial deviation. I just know not to fire a 6th round from another group, that becomes round 1 of the next group on paper. Seems like I have OCD, but I don't. I am a slob typically. It keeps things organized for me and I have seen the rise or fall of a 2 gr bullet change from group to group. It's in the chrono data very clear. I'd rather have 1601, 1601, 1601, 1603, 1602, than 1601, 1612, 1608... etc. If you have the time to invest, why not do the due diligence... if you have the time or patience

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mrbill2 posted this 26 October 2009

When I first noticed the imperfection on the bullet, it was just the size of the point of a pin. Why it caught my eye, just luck. I grabed a lead pencil and poked around the little mark and look what I uncovered.

 

mrbill2

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