Did some experiments on sizer size.....

[Harry O]

Every book on casting says that the same bullet mould will cast different diameters depending on how hard the allow is (due to the mix, not heating and quenching them). In looking at the books, the difference between pure lead and linotype is from less than 0.001" for the largest bullets to considerably less than that on smaller ones. A test of the same bullets that I made from Bhn 6-7 mix, Bhn 12-13 mix, and Bhn 17-18 mix showed this to be true.

I originally decided to do this test, not for the above reason. I wondered what happened when the three different mixes were pushed into a 4500 sizer. I ahve noticed that the diameter that the bullet comes out rarely matches the posted diameter on the die and actually changes with alloys. I was using a bullet that cast between 0.312" and 0.313". I pushed them into the same 0.308" sizer. The difference in diameters after sizing was more than the difference before sizing.

The softest lead came out almost exactly 0.308". The hardest lead was a full 0.309". The other was inbetween (not surprising). That is not much, but it is about twice the difference I measured between the "as cast" diameters.

I have my theory why this is so. It has to do with the differences between the yield strengths of the different alloys and the amount of "spring back" each would have. The greater the yield strength, the greater the spring back. Any other theories?

[felix]

Nope, Harry, you got it! ... felix

[randyrat]

That makes sense now. I have sized bullets and measured them at a later date to find they changed, or at least, i thought they change. Now i know the mistery.

Seams i get about a .0005 diference than the sizer die with WWs and it wasen't different pressure on the caliper.
Spring back makes sense.

[JIMinPHX]

I ordered a custom size Lee push through sizer one time a while back. When I measured the first batch of boolits that I sized with it, they all came out .0010-.0011 over the specified size. I was about ready to start trashing Lee all over this board, but when I took a bore mic & checked it, it turned out that the bore was cut dead on size as far as I could measure. I then tried some boolits that were made out of softer alloys & found that I got the size that I had wanted after all. I don't know how those guys at Lee sell the things they do at the prices they charge.

[Bret4207]

I think you git it. I did te same experiment many years back. Not only will sheer hardness affecty size, so will alloy content. I had 3 different alloys at one time. All were just abiout 12Bhn (within 1 point) and all 3 behaved differently in most aspects- dropped different size, cast differently, sized differntlt. It's one of those odd, but interesting things you notice that seems to expalin a lot of issues.

[mrbill2]

My 308 has a tight throat, .3085. It will not take any bullets over that dia. I had to make push through dies for each alloy I use. I also see a difference between water cooled and air cooled.

[Harry O]

Just so everyone is aware, I use a Sterrett micrometer that goes down to 0.001". It is not one of them that goes down to 0.0001" (I wonder if I could even read one of them). However, the distance between the 0.001" marks is about 1/16" so I can eyeball if it is 0.308", 0.308"plus 1/3, 0.308" plus 2/3; and 0.309", etc.

Based on that, the "as cast" bullets in different hardnesses were about 1/3 to 1/2 of one-thousandth apart. The measurement after sizing was a full thousandth apart.

[leftiye]

Could it be the die springing rather than the lead rebounding after compression? That is the die stretches more with the harder lead, maybe. Steel stretches and recovers better than lead does.

[Harry O]

leftiye: There is no doubt that some of that is going on. However, I believe the amount in the steel die is contributing is very small.

My guess is that the ratio of Modulus of Elasticity for the lead mix and the steel die would tell how much each is stretching/compressing. The steel has a MUCH larger Modulus than lead. That means it will take a whole lot of pressure before it expands/contracts as much as the lead.

[Marlin Hunter]

It sounds like it has to do with the elasticity of the alloy.

[Bret4207]

For whatever reason, this just proves out the "each gun/component is an individual" theory. One guy sizes .358 with his alloy and gets a .358 boolit, another sizes .358 and gets a .3595 boolit. A thou and half can make or break a load. Add in that sizers aren't always bored as marked and it adds even more varition.

Lesson- always see what YOUR components measure, weight, etc.

[Harry O]

I just did a check of Modulus of Elasticity for lead, tin, and steel. In a quick search, I did not find antimony.

Lead is about 1,000,000
Tin is about 10,000,000
Steel is about 30,000,000

The amount of tin in our mix is small so I believe the combination of lead and tin is probably close to 1,000,000. So the lead will move/deflect approx 30 times as much as the steel when both are subjected to the same pressure.



Bret: I have no doubt that what you say about different mixtures that have the same Bhn act differently. I have not done any specific testing to see, but I believe that WHEN THE GUN AND BULLET ARE SIZED PROPERLY, the yield strength is the largest part of the difference between two different mixes, not what little differences there are between the two mixes. When the gun and/or the bullet are NOT sized properly (such as a much larger or smaller cylinder throat than groove size, or a smaller bullet than groove size, etc) all bets are off.

I use the Bhn hardness test to predict yield strength of whatever mix I am using. There is one person on this board who insisted to me that hardness tests ONLY tested hardness and could not be used for anything else (he also said that lead did not have a yield strength and that I could f**k myself since I didn't agree). I worked in a metal fabricating plant for over 20 years. We used a portable hardness tester that was calibrated in PSI for yield strength and for ultimate strength. It was calibrated for low alloy to high alloy steel and we used it for quick and dirty nondestructive tests to decide where we had to cut off a piece and test it in the lab. This tester was available on the open market along with many others calibrated for other types of metals.

The point is, the mixtures that make up steel with yield strengths from 36,000psi to 80,000psi are all different. But they all, being made mostly from iron, were close enough that we could use the same tool to give reasonable answers for all of them. That is what I am doing with the Bhn tests with lead alloys. I am not saying that the Bhn is exact to the fraction of a PSI. I am saying that they give me a strong clue on how it will work in the gun before spending a lot of time and effort testing it.

[leftiye]

Yup, lead will move farther at a given pressure (softer?), but unless I'm mistaken, it springs back very little. Just as brass sticks in chambers because of the same phenomenon. The steel and brass expand together in the chamber when fired, but the brass is less elastic (springs back less) and ends up stuck in the chamber.

[Bret4207]

Harry, I don't even pretend to know WHY some alloys seem to perform better than others. I do know for a fact that different alloys with different characteristics of the same Bhn can act differently. But it's another case of "depends on" scenario cropping up. It might make no difference in 80 out of 100 guns/loads, but it may make a small difference in 15 of those guns/loads and make or break the remaining 5%. It all depends on......