Driving band cracking

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  • Last Post 14 March 2017
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max503 posted this 06 March 2017

These are from a Lee 6 cavity mould.  Bullet weight is 105 grains, SWC, 9mm/38/357 caliber.

A picture is worth 1000 words.

Upon opening the mold, I noticed that the boolits hung up consistently out of two of the cavities.  They had to be tapped or flicked out of the cavity with the aid of a fingernail tip.  During sorting I found about 20-30 % of my precious boolits had cracked front driving bands.  Bummer.

What do I do to keep this from happening?  Polish the cavities, perhaps?  If so, how do I do it? 

FWIW I use a Lee bottom pour pot and Bull Plate lube. 

In my defense I would say that the deep lube groove design of this mold is part of the problem.

Thanks in advance.

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Scearcy posted this 06 March 2017

What is your alloy? 

Jim

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max503 posted this 07 March 2017

About 1/2 lino, the other 1/2 sheathing. Maybe a little ww for good measure. It's fairly hard.

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RicinYakima posted this 07 March 2017

 

"In my defense I would say that the deep lube groove design of this mold is part of the problem."

My estimate is that your antimony to tin balance is a little out, but the biggest problem is your mould is too hot! The bullets are not fully crystalized prior to you opening the mould. The big crystals indicate more than 4 to 1 of antimony, so you have to have time for the tin/lead to get hard before opening the mould.

Consider casting at just 100 degrees above the liquidous temperature, measured, and about 4-5 seconds from pouring to opening.

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45 2.1 posted this 07 March 2017

You're opening the mold too soon with that hot hard alloy. Wait about 6 seconds after the sprue freezes and see if it still happens.

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RicinYakima posted this 07 March 2017

The other thing is that the cavities are cut crooked in the blocks.

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onondaga posted this 07 March 2017

max503 you said,
"About 1/2 lino, the other 1/2 sheathing. Maybe a little ww for good measure. It's fairly hard."
Lino and sheathing at 1:1 yields ~ BHN 15. Adding WW is not a good measure unless you wish to deliberately soften and weaken your lino/sheathing alloy. Your lino/sheathing alloy very closely approximates Hardball Pistol Alloy. Your alloy is sufficient for any load specifying Lyman #2, or Hardball Pistol alloy in all the calibers you list.
The chunking off of alloy from your bullets upon mold opening is completely thermal related.
The safest thing to use to burnish out mold cavity edge,  bullet edge catching flaws is a bamboo BBQ stick used as a rubbing burnisher on the trouble spot and check mold cavity edges under optical magnification of 6-10 power.
Gary

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max503 posted this 07 March 2017

Thanks.  I will try opening the mold later, and burnishing the trouble spots with a skewer.

At least now I know what's causing them dam fliers.

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David Reiss posted this 07 March 2017

I have seen this many times and it is definately a result of the bullet still being too hot upon opening. Early on at the PD we used to have to cast many thousands of bullets, and as such the process was hurried at times, resulting in the condition. Just reduce your heat some or just slow down a little and it will solve this issue. I would do this before doing anything else and I think you will find that nothing else is necessary.

David Reiss - NRA Life Member & PSC Range Member Retired Police Firearms Instructor/Armorer
-Services: Wars Fought, Uprisings Quelled, Bars Emptied, Revolutions Started, Tigers Tamed, Assassinations Plotted, Women Seduced, Governments Run, Gun Appraisals, Lost Treasure Found.
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Tooweels posted this 07 March 2017

Agree with the others its Easy to open the Mould to early, If you can buy another the same and use both the problem will go away, great bullet those made many thousands of them

 

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max503 posted this 07 March 2017

Yes, I was casting at high output, high temp.  I'll slow it down and see if that helps.  No sense making rejects.

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onondaga posted this 08 March 2017

Max, the hardness I listed for your alloy is only when room temp air cooling as cast. Your alloy has high Antimony and is very sensitive to any kind of rapid cooling. exapmle: your bullets chill dropped into water would cause the BHN to soar out of the practical use range for your application, decrease accuracy and increase leading..

 

Gary

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max503 posted this 14 March 2017

Thanks for the help.  I'll give your suggestions a try.

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