Thoughts while sorting boolits

[7br]

What would make a boolit weigh more than the median weight?

It seems like a boolit might be lighter due to internal voids, not having good fill out on the base, and crud in the melt that did not get fluxed out. The only things I could come up with for heavier was not closing the blocks completely and a slightly cooler blocks so the cavities were smaller due to thermal expansion.

Am I missing something else?

[dagger dog]

Exceptional fillout, sprue plate cut with no tearing ?

What were the circumstances that lead to your question ?

When weighing the boolits from a new mold mine usually wind up with the typical bell shape lay out.

[44man]

What would make a boolit weigh more than the median weight?

It seems like a boolit might be lighter due to internal voids, not having good fill out on the base, and crud in the melt that did not get fluxed out. The only things I could come up with for heavier was not closing the blocks completely and a slightly cooler blocks so the cavities were smaller due to thermal expansion.

Am I missing something else?
You have things backwards. Cooler blocks make larger boolits. As a mold gets hotter, cavities get smaller unlike a hole in the center of metal.
You mention many good points that are eliminated with good casting procedures.
Mold temp changes as you cast is what makes weight variances. Colder is heavier and hotter is lighter.
Voids are just not an issue with good casting. I have to wonder about voids, how do you trap air in a boolit? It might happen but I don't know how.

[7br]

I was sorting some RCBS 6mm-95 grain boolits this morning. They were all from the same casting session. They had been visually inspected. I was weighing on a RCBS 502 scale. Most were coming in right at 99gr, but a few were lighter and a few were heavier. Less than 0.1 grains, but it was noticeable. I pre heat my blocks, but I am sure it takes a little bit for the temp to stabilize in the blocks.

I generally do not worry about weighing, but wanted to see how good of a group I could get.

44man, you are correct.

[fryboy]

while mostly an alloy stays alloyed tin does dross out ,especially at higher heat , tin makes the boolit lighter and less tin would make it heavier ... whether or not that would apply in this case i dont know , one would think it would be a negligibly amount/weight at best ...

[HARRYMPOPE]

I had argued about voids not happening with good casting. But last year when visually sorting 30 caliber 180g for a match i saw a small mark on a bullet.(it was on bottom band above the GC)I was able to push a thin piece of wire in about 1/8" or more.it weighed 5g less than the others.I marked the bullet and shot it went out of the group 1.5" at 100 yards.It was the only cull of the 200 i sorted.All others of the lot grouped well.

George

[GLL]

Half of your sample will always be above the "median" weight no matter what the cause!

Jerry

[williamwaco]

I have seen voids but only in the base. Usually directly under the sprue cutoff. I do not mean the hollow torn out by cutting too soon, I mean the base is flat but there is a hollow under the sprue cut. I have occasionally seen them on the base band. Usually noticed because of a pin hole.

There is an old book. I do not remember the title wherein it is proven that all cast bullets have voids. This book displays photos of many bullets cut open lengthwise to show voids the size of a BB and some of them have more than one.


I do not think the author was trying to deceive. I think he was doing something wrong. Those old-timers would not have been shooting the scores they achieved at 800, 900, and 1000 yards in the 1860's if their bullets had been that holey.

I have been looking for a void for many years and have never seen one except in the base. Those are always (in my case) caused by the sprue plate being too tight to vent properly.

When I weigh my rifle bullets I occasionally find one that is 5 grains light on a 170 grain bullet. I usually think "Ah-Ha! I found one." I clamp those bullets in a vise and with a file, file them away to nothing. I have NEVER found a void.

I am not saying it can't happen but I do believe it is very rare.


.

[44man]

I had argued about voids not happening with good casting. But last year when visually sorting 30 caliber 180g for a match i saw a small mark on a bullet.(it was on bottom band above the GC)I was able to push a thin piece of wire in about 1/8" or more.it weighed 5g less than the others.I marked the bullet and shot it went out of the group 1.5" at 100 yards.It was the only cull of the 200 i sorted.All others of the lot grouped well.

George
A void is usually visible at the edge. Never seen one inside a boolit. Lube in a mold can form a gas bubble and so can a lack of air venting or too hot of a spot.
Cold molds that cast in layers are bad.
To have a void in a perfect boolit would be so hard to do I don't think it can happen.

[popper]

0.1% and you are complaining? Are jacketed better? Don't think so.

[SciFiJim]

When you are talking a 1/10th of a grain difference, it is possible to have that by the difference in pressure exerted on the mold by the handles. I have noticed that as I tire in a long casting session, my grip gets looser if I don't pay attention. A looser grip may give a slightly larger boolit. Measure the boolits in question and see if they are larger 90 degrees from the part line than the others.

[rintinglen]

SciFiJim hits a home run, at least in my experience. A while back I found myself doing exactly the same thing. An hour of casting and my hand got a little tired, my grip got a little bit looser. and suddenly, my boolits were out of round by .002 and about 1 1/2 grains heavier. I refer to this as "Unintentional Beagleing."
I have found the occasional void, more commonly on the side than on the base, almost always in a cast from a mold not quite up to temperature, usually in a boolit with incomplete fillout.

[SquirrelHollow]

I was sorting some RCBS 6mm-95 grain boolits this morning. They were all from the same casting session. They had been visually inspected. I was weighing on a RCBS 502 scale. Most were coming in right at 99gr, but a few were lighter and a few were heavier. Less than 0.1 grains, but it was noticeable. I pre heat my blocks, but I am sure it takes a little bit for the temp to stabilize in the blocks.

I generally do not worry about weighing, but wanted to see how good of a group I could get.

44man, you are correct.


When you get into bigger stuff, the weight difference become more obvious. And, different mold block materials and manufacturers' processes can effect how temperature changes the cavity (or cavities).

The alloy you're using can influence temperature effects, as well. High antimony alloys seem to have more 'weight drift' caused by temperature, than other alloys I've worked with.

I have a single-cavity brass mold for a .433" 430 gr bullet, that I use with a high antimony alloy. If the mold is on the cold side of usable, and filled with alloy on the cold side of usable (but still eutectic), it can add up to 9 grains to the intended weight of the bullet. On the flip side - if the mold is hot (nearly overheated), and filled with hot alloy, it can decrease bullet weight by up to 12 grains.


It's an extreme example (in my experience), but there's no room for losing concentration, when working with that mold. Even if the alloy temperature remains stable, a wandering mold temperature will turn all of my efforts into wasted energy (and reject bullets) very quickly.

[popper]

Accuracy: +/- 0.1 grains is the accuracy of the scale. You would need one 10 times better, with NBS certs, to be able to reliably determine the actual weight of your CBs in 0.1 gr.

[captaint]

Last week I poured up some 148 gr Lyman wadcutters. The sprue plate (bought the mold used) is slightly warped and the sprue "cut" holes in the plate aren't cut deep enough. I need to chuck up my countersink and finish the job. Anyway, the diff in weight was from 142.5 gr to about 143.8. Not terrific, but not bad, really. Certainly close enough for my shooting. I don't compete in any kind of bullseye shoots. enjoy Mike