Effect of heat levels on Cast boolits size?

[Texantothecore]

Just thinking about cast boolits and I wondered if anyone has seen a size difference between hotter cast boolits and colder cast boolits. Any thoughts?

[sqlbullet]

hotter casting temps yields smaller boolits as I recall.

[geargnasher]

It really seems to depend, and the different personal experiences of members here will cause some loud arguments.

Generally, with alloys similar to clip-on wheel weights, I've observed that cooler moulds (producing shiny boolits) generally make larger boolits than with the same mould and alloy will when the mould is run hot enough to make boolits with a light, even satin frost all over. Severely frosted, pitted boolits usually are smaller still.

Now, keep in mind that alloy composition, mould material, alloy temperature, mould temperature, and ambient temperature all affect this, and I've found that a certain mould I have casting 20:1 alloy makes larger boolits when run very hot, hot enough to make the sprue puddle stay molten for about six seconds.

Gear

[mooman76]

I agree with geargnasher. I have heard some state that hotter yield smaller bullets but I know for a fact that I had a mould dropping larger bullets as it got hotter. The reason I know this is because I was trying to get my ML boolits to drop smaller. They were minies and suppose to slid down the barrel fairly easy but they weren't. I noticed the first few were dropping smaller but as the mould heated up, they would drop larger and not fit as well. You also have to factor in that the mould is getting hotter and enlarging also.
So I think it depends on the mould along with temp and it could go either way depending on both factors.

[Texantothecore]

Interesting. I brought this up because I have been pouring very hot with a lot of frost on the 405 grain .45-70 bullets (due to the need to get a whole lot of lead volume into the mold) and in a discussion today talking about casting at temperatures below the melting temperature of zinc in order to cause zinc to float to the surface, the thought occurred to me that you could slightly tailor the caliber of the bullet by pouring either hot for smaller bullets and cold for larger bullets. Seems you might be able to move the size by one or two thousandths just by temperature of the incoming molten stream.

Another test project to do over the holidays. I love casting...so much to think about and integrate.

[Texantothecore]

This would also explain some comments that one person's specific mold casts a bit differently than another persons mold. It might just be temperature of the incoming stream plus how hot the mold is kept. The latter might vary by the rhythm of each each different caster and whether they cool the mold down every 3 or 4 casts.

[fishnbob]

I just cast some .452-230 TC boolits about 2 hrs. ago. The frosted boolits ran .450 to .451 and the bright shiny ones were .452 to .4525, much more consistent in diameter and weight. The alloy was 725*, the shiny boolits came from the mold getting too hot. My bad! I didn't drop many frosty ones, I was lookin for it as I cast. I actually was trying out a mold that I removed the bevel from one of the cavities. So I was dropping one flat base and one bevel base.

[williamwaco]

I don't really have a horse in this race. I don't care about as-cast diameter because I am going to size them anyway.

That said, I find lightly to moderately frosted bullets are the same diameter as shiney ones. Severly frosted bullets, so frosted that the driving bands are not fully formed will be one to two thousands smaller.



.

[Texantothecore]

Well, I know what I am going to be doing over Christmas. A study is afoot!

[williamwaco]

Well, I know what I am going to be doing over Christmas. A study is afoot!



Studies are a valuable resource of this board.

Please share your results.



.

[Texantothecore]

I will publish it here. I will spend a few hours this weekend designing the study so that it might of some use to all.

[243winxb]

Hot frosted bullets = smaller in diameter/iron moulds. Lee moulds that are super hot produce larger bullets/mould expands. Less than .001" difference with iron, more with Lee.

[44man]

Gear is correct, nuff said?
The cavity will get smaller as the temps go up, not larger. The cavity is half in one block and half in the other and is different then a hole in a solid block. Expansion is towards the cavity, not away from a hole.
I make my own molds and once in a while a boolit will cast too small with a new one. I can only get the cherry to cut more metal by heating the mold and it is surprising how much metal will be removed.
Your smallest boolit will be with a hard frost.

[45-70 Chevroner]

Metal, when frozen shrinks. When metal is heated it expands, and I guess it expands in all directions. I would take this to mean that the cavity of a mold or mould would become smaller in diameter and even shorter when heated. Then you have to take into account the alloy and depending on the alloy how will it react to different temperatures. One thing I do know is I can cast a batch of boolits today and they will come out a certin diameter and the next time I cast a batch they will come out a little different this would also mean they will problably weigh out a little different. I usually cast a little on the hot side, around 800 degrees. I find at that temp. I get better fill out with my alloy. I know I don't have the answer, but I think every thing I have read above sounds quite viable.

[Texantothecore]

I had wondered about the actual expansion of the mold when hot and it seemed to me that the cavity would close up as the temperature increased.

I will design the study with the intent of it suggesting a method of controlling the size of the bullet.

[runfiverun]

you will need a way to monitor the mold's temperature.
some like to cast with a hotter mold and a colder alloy [675] temp for a reason.

[Texantothecore]

I am just going to monitor with my hand, that should be sufficent. I will vary the temperature by casting rhythm as well as cooling the mold with a wet cloth. It would be better to use an infrared monitor, but they are in short supply.

The closing of the space as it warms might also give some insight into the fact that my rifle shoots extremely accurately after 14 bullets, the barrel is at an estimated 140 degrees at that point. I probably need to throw cooler,larger bullets.

[josper]

I just started using a dig. BBQ thermomitor like NOE was selling. The probe is mounted in the mould.I heat the mould on my hot plate to 400deg. My alloy is set at about 675deg. I have found that some moulds have a narrow window for temp. to produce the bigest dia.boolits. When I keep my mould between 400 and 425 deg I get my best boolits .460-.461 For my 45-70. Since I started using this meathod I'm getting near perfect boolits from the first drop. Before this I was casting until the boolits started to frost and I ended up with a bunch that were.458 NO MORE!!

[Texantothecore]

I will write up and publish the proposed study before I do it. I hope you guys can make suggestions that will make it more useful.

[geargnasher]

you will need a way to monitor the mold's temperature.
some like to cast with a hotter mold and a colder alloy [675] temp for a reason. Very much true.


Gear is correct, nuff said?
The cavity will get smaller as the temps go up, not larger. The cavity is half in one block and half in the other and is different then a hole in a solid block. Expansion is towards the cavity, not away from a hole.
I make my own molds and once in a while a boolit will cast too small with a new one. I can only get the cherry to cut more metal by heating the mold and it is surprising how much metal will be removed.
Your smallest boolit will be with a hard frost.

If you aren't familiar with the properties of metals it's difficult to imagine which way the cavities move, but you know how it works!

Gear

[RegCom7]

Your proposed study sounds interesting, Texantothecore. Maybe you could try it with a cold temperature, and then a hot temperature with both iron and aluminum moulds. Such as 700 degrees compared to 800 degrees. And maybe try it with pure lead, and WW, and also a harder alloy.

[243winxb]

Saw a pot that run to hot, over heating the alloy. The caster was using an aluminum mould. The boolits got larger in size. If i remember correctly, around 1200 degrees??

[Texantothecore]

I ma not sure what would happen at 1200, but it could hurt the mold as aluminum melts at 1220 F. That pot would give you a sun tan!

[josper]

An aluminum mould that I bought had a warning in the instructions not to heat the mould beond 600deg as it could damage the mould.

[Iron Mike Golf]

I had wondered about the actual expansion of the mold when hot and it seemed to me that the cavity would close up as the temperature increased.

I will design the study with the intent of it suggesting a method of controlling the size of the bullet.

I thought back to a demonstration in 8th grade science class. The teacher had a cast iron donut and a cast iron ball, each mounted on a handle. The diameter of the donut hole was just too small to let the ball pass through it. He heated the donut in a bunsen burner flame for a minute. He tried to push the ball through and this time it went through the hole. He heated both the donut and the ball in the flame and once again the ball would not pass through.

Thermal expansion happens in all dimensions. Think of it as scaling up the mold block. The cavity scales up the same proportion as the length, width, and height of the block.