Double cavity woes

[SCHUETZENBOOMER]

I recently aquired a nice Lyman 375248 double cavity mold. I can not for the life of me cast two at once. I have tried both a lyman dipper and Rowell ladle. Either side casts beautifully when cast singly. Any time I try for a double I get a great first pour and unfilled second pour. Mold and lead are up to temp. 20:1 alloy.
I tried "chasing" the vent lines with a carbide scriber......same results. I loosened the sprue plate a bit....same results. I have cast in every conceivable postion....same results. Sure seems like a venting issue to me.

Thoughts?

[mpmarty]

Bottom Pour!:drinks:

[44man]

What is "up to temp?" 20 to 1 needs about 800*. You are most likely way too cold.

[SCHUETZENBOOMER]

I have cast several hundred "perfect" boolits from .440 roundballs to 500gr 45's in the last few months....all at 680deg or so on my Lyman t-meter. I checked the thermometer in boiling water and was within a couple degrees (at 1000ft elev).

Why would temp be the issue if I am getting perfect fillout when cast (either side), even with a full load in the Rowell ladle?

[Doc Highwall]

It could be that once one cavity is filled there is less venting for the second cavity and the higher temperature will help it flow better.

[SCHUETZENBOOMER]

Doc,

Thanx for the description of the above tip. Makes sense. Not sure I can get the lead up to 800 on my current setup. It's an old LP "hand warmer" I made for Buck Camp.

[beagle]

You're mould is getting too hot. Slow down the casting tempo. The mould blocks are not big enough to dissipate the heat generated by two .375" heavy weight bullets.

I had Walt Melander at NEI make a DC .375 in meehanite once with different cavities over 300 grains in it and he said it will never cast as the blocks would overheat and I'd get incomplete fillout. I had him go ahead with the idea of casting alternate cavities and he said that would work.

He made it, I tried both cavities at once and got incomplete filling as he said would happen. I cast alternate cavities and it works well.

He had a computer program and punched in block cube, bullet weight and diameter and number of cavities and it told him yes/no. Handy program to have.

When I'm running them fast, I have several DC 429421 moulds that do the same thing./beagle

[anachronism]

Lightly chamfer the mould block parting line so you have a VERY SMALL bevel on both blocks to assist venting. Then cast each cavity individually, that means pour the front cavity & give it a second to freeze, then refill the ladle with fresh alloy from the pot & pour the second cavity. As you start each cavity, try briefly touching the ladles nozzle firmly in the sprue countersink as the cavity fills, then pull it away & allow the entire contents of the ladle to drain over the sorue, being careful not to get any allow in the second cavity. Try tilting the mould forward a bit to prevent this. Then do the same with the second cavity. I cast many, many heavyweight bullets (300+ grains), and this always works for me, once the moulds are at normal casting temp.

[Doc Highwall]

With my two cavity moulds I have no problem with a 30:1 alloy at 775-800 Deg with a bottom pour. You do have to find the right flow rate and when you do every thing goes great. Anachronism mentioned about the edge break and I will mention the screw for the sprew plate, this is another thing that will trap air causing bad fill-out on the second cavity if they are to tight. The sprew when it starts to cool pulls the sprew plate down as you are pouring the second cavity. ask me how I know.

[HangFireW8]

I agree, it is a venting problem. The best vent for each cavity is the other cavity. If that is blocked, insufficient venting.

I had a similar problem with a 45/70 mold where the cavities were very close together. The problem was the second pour cavity was venting into the first while the first was still molten. As a result the first boolit always got a flat spot on it, and always on the mold line on the side of the second. The flat spot was from the air escaping from the second cavity, just as the alloy was about to solidify.

For me, allowing the vent lines between the two cavities to become clogged, and waiting a few more seconds for the first boolit to solidify before pouring the second, fixed the problem.

In your case, you are waiting long enough that this isn't a problem, but your mold is too tight to vent elsewhere.

http://castboolits.gunloads.com/picture.php?albumid=274&pictureid=1830

-HF

[HORNET]

On most double cavity molds, I find that it helps to cut a vent groove between the cavities and parallel to them. This allows the air to escape from the second cavity when the first cavity has a boolit in it blocking the vents. Look at most 4+ cavity molds and you'll see the same kind of venting. It usually helps.
I've got an old 375248 double cavity and the distance between the cavities is only about .090" IIRC. I did the additional venting that I described above on it and it made a slight improvement but did NOT fully correct the problem. I think the mold material between the cavities is just too thin and there is just too much localized overheating. I gave up and just run it as a single cavity. I get just about as much production. Trying it as a double, I think the overall heat input rate was higher than the cooling ability of the blocks.
Joe Brennan did some research a couple of years ago on mold surface area vs. boolit weight for ease of casting. I believe he's got the results in the latest version of his book. It's available free on-line somewhere but I don't have my reference info handy.

[SCHUETZENBOOMER]

Lot's of good info here. I will try some suggestions this weekend. With the thousands of multi-cavity molds out there in Boolit-land, I figured it had to be me doing something wrong. I like the idea of waiting a bit on the 2nd pour.

I am all ears and learn more everytime I cast. Looks like I need to throw another 100 degress at the leadpot. I do not think I have ever gotten over 700 degrees and have had what I will call excellent results. Last weekend with that Lyman 375248 double cavity mold I cast nearly 150 boolits (one at a time). Later, I separated the bullets by weight into 2 lots of +/-.2gr and threw 5 back into the pot. I had about an even split of 249 1/2gr+/-.2gr and 250gr +/-.2gr.........all weighed on my beam scale one stinking boolit at a time.

MikeC

[HangFireW8]

Looks like I need to throw another 100 degress at the leadpot.

You mentioned you were using 1:20. High tin alloys don't need as much heat as WW based alloys, if you start getting long whiskers and fins back off the heat.

But by all means try more heat, and less, keep trying stuff until you get it figured out.

-HF

[SCHUETZENBOOMER]

I was getting vent-whiskers so I did back off a bit.....to probably 660-680 on my thermometer. That is one of the reasons the 800 deg suggestion kept throwing me.

[HangFireW8]

I was getting vent-whiskers so I did back off a bit.....to probably 660-680 on my thermometer. That is one of the reasons the 800 deg suggestion kept throwing me.

I've never needed to go to 800, might be needed for a nearly pure lead mix with next to no tin in it. I would try it if I thought an alloy needed it, after all there is a bit of mystery in the content of every alloy we make, and if the usual doesn't work, try something else...

-HF

[Lloyd Smale]

correct answer. I cast alot of 50s and 475s and its a struggle with some molds. They tend not to fill out between the two cavitys where the metal is the thinnest. It tends to be even worse with a high tin alloy. You have two options. Either cast it as a one cavity molds or slow way down and use something like a bowl of water or a wet rag to keep your mold cool enought. Its a ballancing act but it can be done. Ive got quite a few ballistic cast molds in those calibers and what i ended up doing was ordering them as 3 cavity molds in 4 cav blocks and doing two plain bases on the outside and a gas checked version on the inside. when i cast them i either cast them as a 2 cav plain base or a single cav gas check mold and casting fewer cavitys along with the bigger blocks takes care of the problem. this way also allows you to keep the temp up on your pot.
You're mould is getting too hot. Slow down the casting tempo. The mould blocks are not big enough to dissipate the heat generated by two .375" heavy weight bullets.

I had Walt Melander at NEI make a DC .375 in meehanite once with different cavities over 300 grains in it and he said it will never cast as the blocks would overheat and I'd get incomplete fillout. I had him go ahead with the idea of casting alternate cavities and he said that would work.

He made it, I tried both cavities at once and got incomplete filling as he said would happen. I cast alternate cavities and it works well.

He had a computer program and punched in block cube, bullet weight and diameter and number of cavities and it told him yes/no. Handy program to have.

When I'm running them fast, I have several DC 429421 moulds that do the same thing./beagle

[Shiloh]

It could be that once one cavity is filled there is less venting for the second cavity and the higher temperature will help it flow better.

This has worked for me. A brief pause before filling the second cavity may produce a quality, boolit by allowing the first to set. This prevent air from being displaced onto the still molten first boolit.

Shiloh

[Doc Highwall]

You can fill the first cavity faster then the second cavity. On temperatures try working in 25 degree increments not 50-100 degree increments then write notes as to the mould, alloy and temperature used.

[skeet1]

schuetzenboomer,
When you are using your dipper are you holding the dipper tight against the mold (small sprue) or are you holding it away forming an nice little puddle on top of the sprue plate. If you are not forming the small puddle try it.

Skeet1