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Discussion Starter · #1 ·
I PC'd, sized and weight seiparated 9-122gr TC bullets today. The lot of bullets was cast with equal amounts from different ingots to standardize the hardness and the lead was stirred. The volume of lead was kept high but I didn't use a thermometer. The bullets grouped from 124gr/126gr/128gr, 129gr, and 131gr. with the bell curve mostly at the 126 and 128gr weight and tapering off at 124gr and 131gr. I culled out maybe 10% of my bullets with exposed lead from the resizing. Any answers as to why there is such a wide weight variation? Heat?
 

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Shrinkage porosity and variations in the thickness of your powder coating.

Try pouring a larger sprue, overflowing each cavity, coupled with better visual inspection and then weigh a sample before and after powder coating.
 

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mold temperature.
your shiny ones are the light ones.
 

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speed.
think about your alloy as heat.
your looking to get the mold temp up to about 400-F this allows the alloy to flow and fill out the mold better.
once you get it there you make either 3 or 4 pours a minute to maintain that temperature.
i call it cruise speed.
you fill, count, open, fill count.
the count is the wait time for the sprue to harden.
how hard it is to open the mold is the feeling that gives you the clue as to the molds temp.
too hard to cut= too cold
smears=too soon/too hot.
your feeling it and maintaining that feel.
 
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Discussion Starter · #8 ·
Thanks. Another question. I want to cast as many bullets as possible yet need to keep my mold temperature in control as you suggest. Would alternative between molds work?

I'm concerned about the how much the pot is filled too just like a powder thrower. Maybe fully filled pots cast heavier bullets? At what level do you maintain your lead level? I'd guess you don't run you pot to empty if you are using a bottom fill pot.
 

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didn't see this sorry.
Thanks. Another question. I want to cast as many bullets as possible yet need to keep my mold temperature in control as you suggest. Would alternative between molds work?

I'm concerned about the how much the pot is filled too just like a powder thrower. Maybe fully filled pots cast heavier bullets? At what level do you maintain your lead level? I'd guess you don't run you pot to empty if you are using a bottom fill pot.
i keep my pots full all the time, that way i maintain the same head pressure on the spout.
i also use 40 lb. commercial pots so a 1.5 lb. ingot changes nothing as far as temperature is concerned.

now a 20 [17] lb. lee will drop a good 20 degrees with a room temp 1 lb ingot and will take a few minutes to regain your alloy temperature.
pre-heat the ingot on the edge of the pot, this cut's the time drastically.
another thing about the lee pots is they will raise your alloy temperature as the get lower and lower.

since your not pressure pouring into the mold how much is in the pot has no bearing on weight.

a short list of things that will affect weight.

1 alloy.
more stuff besides lead will affect the final weight.

2 how well your filling the mold.
crisp clean square edges will be heavier than round or wrinkled bullets.
there is more alloy in the cavity so they are heavier.

3. voids will reduce the weight.
yep air bubbles or cavities from the alloy not being able to suck down and fill the mold properly as the bullet tries to suck in more alloy as the bullet cools.
sprue too small, sprue plate cold, poor venting.

4. cold mold.
see number 2 and 3 above.

you have other things that can happen such as poor venting or hot spots or drips of cool alloy getting in the mold before the hot alloy.
 
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