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Very Hot Topic (More than 25 Replies) Dip-Casting Bullet Weight Experiments (Read 3237 times)
Cat_Whisperer
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Re: Dip-Casting Bullet Weight Experiments
Reply #15 - Mar 19th, 2017 at 8:16am
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texasmac wrote on Mar 19th, 2017 at 12:33am:
I posted ...  There is a possibility that some of the weight changes could be related to a temperature stratification issue, but there’s no question that the percentage of tin in the alloy dropped throughout the casting sessions when the pot was not stirred.  Regardless, stirring the alloy still applies.

Wayne


Consider the cooling of the mould during the 'extra' time spent when stirring.  Hot mould = smaller cavity (the mould metal has to go somewhere when it expands).

VERIFY the percentage of tin in the product at the beginning and at the end.
  

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Re: Dip-Casting Bullet Weight Experiments
Reply #16 - Mar 19th, 2017 at 2:05pm
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CW I was some what confused in regards to the alloy expanding and needing some where to go when it actually shrinks as it starts to cool. Could you please expand on what you feel is taking place with the alloy with a little more detail. The rate / amount of shrinkage and its affects is something seldom disscused yet it also plays an important part in obtaining quality bullets.

I think you might have been reffering to the mould body exspanding and possibly not the alloy if so please please ignore my miss understanding of your comment but in that case
a hot mould would equal larger cavity and not smaller would it not.

JLouis
« Last Edit: Mar 19th, 2017 at 2:13pm by J Louis »  
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Re: Dip-Casting Bullet Weight Experiments
Reply #17 - Mar 20th, 2017 at 7:44am
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Cat_Whisperer wrote on Mar 19th, 2017 at 8:16am:
[quote author=6D7C61786A74787A190 link=1489802900/13#13 date=1489898030]

Consider the cooling of the mould during the 'extra' time spent when stirring.  Hot mould = smaller cavity (the mould metal has to go somewhere when it expands).


Hot mould = bigger cavity. That is why we heat up rings, sleeves, etc for a pressed fit.
  
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Re: Dip-Casting Bullet Weight Experiments
Reply #18 - Mar 20th, 2017 at 8:37am
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Lead / tin alloys always shrink as they cool. Linotype, Monotype and most of the harder antimony alloys shrink much less. That is what those alloys were designed to do shrink very little. Neither grows.
Learning to cast with a dipper is a matter of rhythm and filling the dipper to the same level every time. How hot to run a mold depends on how big the mold is the bigger the block the more heat it will hold and the longer you will have to wait for the metal to harden and shrink so it will drop from the mold. I am against cooling molds with wet rags or other means. Just run the mold at the pace it wants to go at. If you have to wait a long time or the bullet sticks and doesn’t want to drop then bring down the temperature a little. A .25 caliber cavity and a .45 caliber cavity in the same size mold block will want to cast at different temperatures.

40 Rod
  
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Re: Dip-Casting Bullet Weight Experiments
Reply #19 - Mar 20th, 2017 at 9:30am
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bpsmoke wrote on Mar 20th, 2017 at 7:44am:
Cat_Whisperer wrote on Mar 19th, 2017 at 8:16am:
[quote author=6D7C61786A74787A190 link=1489802900/13#13 date=1489898030]

Consider the cooling of the mould during the 'extra' time spent when stirring.  Hot mould = smaller cavity (the mould metal has to go somewhere when it expands).


Hot mould = bigger cavity. That is why we heat up rings, sleeves, etc for a pressed fit.


If you have a large ring (as a ring gear that goes around the flywheel) heating it up expands the meta and the whole ring gets larger and it slips on/off the flywheel.

BUT if you have a large mass with a hole in it the metal when heated will actually reduce the size of the hole.  Demonstrated in classic high school physics demo - 1" ring with 1/2" hole through which the 1/2" ball bearing just passes.  heat the ring up and the ball won't pass - until the ring cools.
  

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Re: Dip-Casting Bullet Weight Experiments
Reply #20 - Mar 20th, 2017 at 10:44am
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Cat_Whisperer wrote on Mar 20th, 2017 at 9:30am:
bpsmoke wrote on Mar 20th, 2017 at 7:44am:
Cat_Whisperer wrote on Mar 19th, 2017 at 8:16am:
[quote author=6D7C61786A74787A190 link=1489802900/13#13 date=1489898030]

Consider the cooling of the mould during the 'extra' time spent when stirring.  Hot mould = smaller cavity (the mould metal has to go somewhere when it expands).


Hot mould = bigger cavity. That is why we heat up rings, sleeves, etc for a pressed fit.


If you have a large ring (as a ring gear that goes around the flywheel) heating it up expands the meta and the whole ring gets larger and it slips on/off the flywheel.

BUT if you have a large mass with a hole in it the metal when heated will actually reduce the size of the hole.  Demonstrated in classic high school physics demo - 1" ring with 1/2" hole through which the 1/2" ball bearing just passes.  heat the ring up and the ball won't pass - until the ring cools.


Take a large plate with a small hole and heat the area around the hole (localized heat) and it will get smaller. Uniform heat and it gets bigger.

We did a similar test, but we heated ball not the ring
  
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Re: Dip-Casting Bullet Weight Experiments
Reply #21 - Mar 20th, 2017 at 1:56pm
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SO, the definitive test here is to measure the temperature of the mould and to cast bullets with the alloy at a constant temperature.

Will the mould make larger or smaller bullets when the mould is hotter?

Will the bullets be equally 'round'?

Place your bets.

  

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Re: Dip-Casting Bullet Weight Experiments
Reply #22 - Mar 20th, 2017 at 7:23pm
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You may be right about mould cavities

As soon as you open the mould it no longer is  a block with a hole in it. It is 2 halves and now the cavity is the outside of each of the halves. The diameter at the seam would probably be smaller by, in the neighborhood of, 2x the expansion of the faces. Also, will be less round with the diameter at 45° (the diagonals of the block) the worst.





  
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Re: Dip-Casting Bullet Weight Experiments
Reply #23 - Mar 20th, 2017 at 7:57pm
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What constant would be used for the hole and how would it be derived. The bullet would be smaller just based on alloy shrinkage regardless of the mould temp.
What would be an acceptable equal roundness be considered.

JLouis
  
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Re: Dip-Casting Bullet Weight Experiments
Reply #24 - Mar 20th, 2017 at 9:13pm
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Let me make a measured observation.

I'm not sure if the difference will be measurable.  It likely exists.  So the real test for me will be measuring (with thermocouples) the temperatures of the alloy and that of the mould. (And then measuring the difference in bullet weights.)

My measurements today involved taking a 1/8" thick disk (OK, 1" would have been better) that was 2-1/2" in diameter.  I drilled a 0.282 or so hole in the center and measured it at 'room' temperature and at some temperature elevated by a propane torch.   

Hmmmmm.  NO difference because of the variability in making the measurements with a digital caliper.  Too much variation of measurement doing it by hand.  Perhaps with plug gauges.



« Last Edit: Mar 20th, 2017 at 9:25pm by Cat_Whisperer »  

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Re: Dip-Casting Bullet Weight Experiments
Reply #25 - Mar 20th, 2017 at 11:03pm
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Cat_Whisperer wrote on Mar 20th, 2017 at 1:56pm:
SO, the definitive test here is to measure the temperature of the mould and to cast bullets with the alloy at a constant temperature.

Will the mould make larger or smaller bullets when the mould is hotter?

Will the bullets be equally 'round'?

Place your bets.



Never thought to keep track of that,   But  variations start at about 4 degrees too hot or cold.  Not sure there is a consistentancy in heavier or lighter either way.
  

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Re: Dip-Casting Bullet Weight Experiments
Reply #26 - Mar 21st, 2017 at 5:54am
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   Coefficients of thermal expansion, in parts/million/deg C at the approximate temperatures of bullet casting:   (X 1.8 for deg F)

Aluminum           28
Brass                 20
Iron                   15
Lead                  30 

   Thermal conductivity, cal/second/cubic centimeter/deg C

Aluminum           0.65
Brass                 0.27
Iron (steel)         0.12
Lead                  0.08

   The thermal conductivity of these metals is such that temperature gradients in bullet mould blocks should be pretty-much negligible at usual casting tempo, say 2-3 bullets/minute.

CHRIS
RGChristensen
  
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Re: Dip-Casting Bullet Weight Experiments
Reply #27 - Mar 21st, 2017 at 10:05am
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rgchristensen wrote on Mar 21st, 2017 at 5:54am:
  ...

   The thermal conductivity of these metals is such that temperature gradients in bullet mould blocks should be pretty-much negligible at usual casting tempo, say 2-3 bullets/minute.

CHRIS
RGChristensen


Hence my question of the difference being from casting at a steady rate and pausing for a few moments to stir as being a possible cause of variation.


  

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Re: Dip-Casting Bullet Weight Experiments
Reply #28 - Mar 21st, 2017 at 4:13pm
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I tried to find temp stratification in my 20@ Lyman pot.  I couldn't.  Biggest single factor is mold temp, mold temp, mold temp. After years of experiments, once I discovered that, I quit weighing; now just cast and shoot  Grin
  

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Re: Dip-Casting Bullet Weight Experiments
Reply #29 - Mar 21st, 2017 at 5:20pm
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