Air bubble in bullet.

[fido]

Hi I have a Seaco bottom pour and a lyman mould for my 44, sraight WW no thermometer. I am new to casting.

If I hold the mould up to the bottom pour spout I seem to get a bubble where the sprue is cut off. This starts happening part way through the session.

If I hold the mould close but not touching the spout it works better as far as no air bubble.

Is this normal? I would rather hold the mould up to the spout it is easier and seems to make a sharper edge on the bottom of the bullet rather than a radiuses edge indicating a better fill.

I have tried different heat settings, the spout freezes if the temp gets too low most of what I have casted thus far are frosty, so I think I am hot enough.

It seems like the mould sprue plate is cooling off the spout causing a partial freeze while the bullet is finishing filling, since it doesn’t do it when the mould doesn't touch the spout.
I would appreciate any input.
Stephen

[garandsrus]

Fido,

My experience is that if lead is flowing through the spout, it's not going to freeze. It will only freeze between bullets.

I have poured some bullets with the mold up agains the spout and it worked well. I think the trick is to hold the flow open a little longer (another second or two) than what you are. This will allow molten lead to still be in the sprue while the bullet is cooling/solidifying. After that you can stop the flow and remove the mold. When I cast this way I only have a very small amount of lead in the sprue hole but the bullet is filled out completely.

Another option is to pour like you are doing, but keep pouring as you pull the mold away so that you get a puddle on the sprue plate. This does the same thing, provide enough material so that as the bullet base cools and shrinks, it has lead to fill where it shrunk.

The sprue releases from the mold a little easier with the second method.

John

[JohnH]

It's possible, though I'm not sure how likely, that the air bubble is air that is trapped because you are holding the mold too tightly against the the pour spout. Only some experimentation will tell. As you pour, the air in the mold must escape. Once the melt is between the last vent line on the blocks and the sprue plate, the only place it has to go is out between the sprue plate and the top of the mold. If you are holding the mold tightly against the pour spout, the last bit of air can't escape. I've experienced this same thing with sprue plates that are too tight. I've used bottom pour for years, I hold the mold 1/2" to 1" below the pour spout, let a god dollop of a sprue develop and them don't cut it for as much as 5 seconds.

[fido]

The air vent thing sounds like what is happening. I will leave a gap when filling.
Thanks guys.
Stephen

[bmblong]

I don't know if you can adjust the flow rate on your pot but I had the same problem with my Lee bottom pour pot. I slowed the flow rate way down and leave about 1/4 inch between the mold and spigot.

[fido]

The pot has an adjustable stop. I have tryed slow and fast. I may have to try that again though.
Thanks
Stephen