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Two cavity mold casting technique

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StewartLeach

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I recently began using a two cavity Lee round ball mold, and was initially disappointed with the results. I do a lot of match shooting, and am picky about ball quality. Balls are hand inspected for obvious flaws, then weighed. Balls more than one half the standard deviation from the mean are rejected. Stats are based on samples of fifty or more balls from each mold.

I have had excellent results from Lee single cavity molds, and was surprised at how many from the two cavity mold went into the re-melt can. Began to think it was my technique rather than the mold. Casting one at a time- only filling one chamber- produced good balls. Had to be me!

I had been casting by filling the chamber farthest from the handles, then moving the dipper spout over to the near chamber. Keeping an eye on the balls as they fell out and sorting revealed the second ball was often poorly formed and light.

Tried a second technique- hold mold vertical, dipper spout placed at sprue hole, then rotate to fill, then tilt vertical again and move dipper to second chamber. Number of visual rejects and weight rejects went down, but still higher than results with single cavity molds.

Third technique was to hold mold vertical, tilt and fill first chamber, then return dipper to pot for a fresh load of metal to fill the second chamber. Excellent results, in line with single chamber mold.

My theory is that in the first two techniques the dipper of metal cools just enough while filling and overpouring the first chamber that it isn't hot enough to flow properly into the second chamber.

The two scoops of metal and individual pours technique is slower than one filling of the dipper, but only opening the mold once for two balls and the lower reject rate result in higher net production than with the single cavity mold.

Comments please!
 
Interesting - I found the same problem to occur ... also ... most of the time one of two balls will fall easily out of the mold, but the second has to be removed with help of some pliers or something ...
 
I truly appreciate your detail and desired results.
Your right, it's all about the temp.
Those darn aluminum molds can be very fussy
The casting rhythm is part of it. I try to make the pour/drop rate very quick. 5-7 seconds in the repeat process, ya gotta keep things moving. Even 10 seconds can mess things up.
The large Lyman dipper is better than smaller spoons.
At that rate I need a break every few minutes.
(just for my hands to recover and wipe the sweat from my brow!!)
Pour, knock, drop, pour, knock, drop,,repeat,,
I have found that ambient temp is a big issue for me.
I cast outside for all of the obvious reasons. All I have is an unheated garage. I use a coleman stove, a cast iron pot and pre-cast muffin tin sized stock to feed my pot as needed,, trying to keep the process the same throughout.
Ambient temp (my environment) is a big deal too. I have better control of the temp variables when it's around 40-50,, if I try to cast when it's 30 degrees or colder outside or 90 in the summer it's much tougher to get reasonable keep rates during the cast.
So I set-up in the spring an again in the fall if I need to,, to make seasonal casting "sessions". I may spend 3-4hrs each afternoon/evening for a few days starting and preforming a cast.

I've found a much higher retain rate when I sit down and cast,, with casting as my job for the week,, then casting 100 or so whenever I feel like it.
Ambient temps or a controlled environment matter as it directly effects melt, spoon, pour and die temp control.
 
Generally I just go fast as I can to keep the mould hot. I've seen people fuss allot to make things perfect but the more they fuss, the more they loose heat. Have everything within reach you might need. A few tools, lead to add to the pot or whatever. Preheat the mould too to cut time in the beginning.
 
The casting rhythm is part of it.

Not just part of it, nearly ALL of it. Make sure the entire mould is hot. I lay on top of the pot or even float in the moulten lead to make sure it is up to temp. First few casts are likely to be discards. Develop that rhythm and keep going. Double cavity moulds can be just fine. That said, my preference is for single cavity moulds. The production rate is not that much less and they are easier to work with and cheaper to buy at the beginning.
 
I like the Lee aluminum molds and have several double cavity ones. I get great uniformity from these molds but they DO have to be kept HOT. I find that fast casting doesn't necessarily keep these molds hot enough. Iron molds do hold heat much better and I use both.
 
I don't use a ladle....I use a bottom pour pot...Fast rhythm, no problems...

It stands to reason that when using a double cavity mold, your number of rejects will double as does your production.....The advantage is time.

When you start casting with six cavity or larger molds, things can be all together different.
 
I never have but many people use a hot plate to preheat the mould or keep it hot. I just either sit it on the edge of the pot while it is heating up or dip the corner of the mould to include the sprue plate into the molten lead for like a count to 24.
 
When I get a new lee mold I have that trouble. Go through the regular trials of filling and many times I have to reject 1/2 or so.

One thing I do is check the sprue cutting holes. For some reason when I have a lot of rejects in a new mold I run a Philips screwdriver into the pour holes to kinda enlarge, smooth out, clean out etc. Have done it with several recent molds ..last one a 450 conical for a cap and ball. Before, 1/2 reject rate,after less than 10% reject rate. Lead just seems to flow better for filing after I do rhis.
 
Rifleman1776 said:
That said, my preference is for single cavity moulds.
Yeah me too, I have a few steel Lyman and RCBS around,,
But Lee doesn't even make a single ball mold for us ML guy's anymore,, they're all doubles unless you can find one used. Trouble is by the time someone is selling a Lee or even a T/C single mold today,, they're shot!! :idunno:
 
Although I have molds from at least half a dozen makers, Lee molds cast the vast majority of ball that I load and shoot. I do have a Lee single cavity mold; it is a .600" mold and really must be kept hot to cast good ball. I frequently rest the mold on the pot to keep it heated.
 
Adui said:
Im a novice, but i have to wonder if a hotplate just to set the mold on wouldnt be a good idea
I've always "floated" my Lee moulds atop the lead pot to preheat them enough to produce proper results the first cast. Never considered a hotplate for single or double cavity molds UNTIL I got a 6 cavity mold. NOW a hotplate is mandatory.
 
Pour, knock, drop, pour, knock, drop,,repeat,,

Careful with that "knock" part. :nono:
There are two knocks in the process. First you knock open the top gate that cuts off the sprue. Then, if needed, you can knock out a stuck ball. But, and that is a big BUT do not hit the mould, just hit the hinge bolt. Buy whacking the hot mould you could distort it.
 
Yep, you are so right!
I had to learn that one the hard way. I near beat to death my first Lee mold,, well I did actually, I ruined it.
 
The legendary mould maker Paul Jones had a routine that he recommended for correct way to open and drop the cast bullet from a mould. It started by tapping the hinge pivot bolt with the mould closed, then placing the mould mallet or whatever your using against the bottom corner of the mould and applying pressure as you open the mould. Typically this will allow the bullet to drop free. If it doesn't then another tap on the hinge bolt should do the job.

Personally I found the placing pressure on the bottom corner of the mould a cumbersome and difficult step. It does seem work though if you can make it work into your routine.
 
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