Boolit weight variation

[jeepvet]

Had a not so good day casting today. Sat down at the pot and casted several hundred Lee C312-155-2R. Had some problems with wrinkles but heated the mold up and pretty much solved that. But I sat down at the scale tonight to weight the little boogers (as cast) and got a shock. The boolits ranged from 156.0gr to 160.4gr. They were pretty much strung out over the range but maybe a few more on the heavier end ( 155.5 - 160.4). I did reload the pot one time during the session but from the same batch of ww muffins. Most of the time the temp was around 750. No frosty bullets, almost all completely filled.

Any ideas on how to keep this from happening in the future? I must confess, I have not read through all of the posts, so if I missed the answer in an earlier post, please forgive my laziness.

[jeepvet]

Ok, found the thread by goodsteel titled "How consistent are you REALLY???" Answering most of my questions. But any specific responses would still be appreciated.

[MBTcustom]

I think it all comes down to three things (the holy trinity of boolit casting if you will)
1. mold temperature
2. pot temperature
3. casting cadence
Make these three the same every time, and you get closer to where you want to be.

If you are getting wrinkles, then the mold has oil in it, or it is way too cold.
I think a lot of new casters don't realize how hot the mold really has to be in order to start getting good results. The mold should be so hot that after the sprue freezes, you can cut it with a gloved thumb (it's similar motion to snapping your fingers, but slowly). Some people palm the sprue plate and keep downward pressure as it cuts to aid with a clean base, and to preserve the sprue plate fit.
The alloy needs to be between 650 and 775 degrees F. If you follow the method I laid out in my thread, you will be able to quickly discover what temperature the alloy needs to be, how fast you need to run the mold, and what the ideal target weight of that mold, with that alloy is.

[runfiverun]

they all influence the other.
if your mold is getting too hot, slow down [cadence] or turn down the alloy temp.
if you are casting quickly but can't keep the mold up to temp, turn up the heat on the pot some or heat the mold more.

now that it's confusing, pick some numbers to start working with.
a mold temp of 375 [steel] to 425 [aluminum]
and an alloy temp of 675 to 750 should cover the whole range.
the only other option is to cool the mold down as you go along, this allows you to keep your cadence up and mediate your molds temperature.

now that I made it worse.
the reason why you wanna keep things in a range is because that will tighten your weight variations.

imagine the difference between starting out with a mold that is 380 and your alloy settled down to 725.
you keep the mold between 370 and 390 during the run and your alloy between 715 and 730 even when adding more alloy to the pot.
you then count out your time of waiting for the sprue to harden, monitor your fill rate [and how each cavity is filled] and maintain a steady even grip on the handles throughout the whole run.
and what your last casting session was really like.

[milrifle]

I'm certainly no expert here, so take this with a grain of salt. I used to have wild fluctuations in bullet weight. I also used to have wild fluctuations in pot temperature. My Lee bottom pour seemed to vary all over the place. Then I built a pid controller. My rejects due to weight variation went from double digits to practically nil.

[jeepvet]

Thanks guys for all of the suggestions and knowledge. I never heard of a PID until this so I started looking at it and decided that I don't know how you can cast without one. I knew that mold temp is important but had no idea how to tell except by boolit appearance. Still seems to be very subjective but I understand a little more now. My understanding about cadence is that it's importance is more to keep mold temp more constant.

Amazing that there is so much more to casting boolits than melting some lead and pouring it into a mold. It is also encouraging to know that even smart people have issues sometimes. Thanks for all of the help.

[fredj338]

In smaller bullets like that, I would expect 1-2gr variation max. The larger the bullet, the greater the variation. As noted, temps matter, a lot. Alos using the same technique matters; direct pour, pressure casting swirling, use the same technique each time.

[44man]

I spent too much time weighing boolits, found with large calibers it means nothing at all by group shooting. Tiny boolits should be kept more even.
My large cast never go near a scale anymore.