Base Porosity

[Don Sarkisian]

What are the contributing factors to cast bullet base porosity and what precautions need to be taken to avoid same.

Thanks,
Don

[HangFireW8]

What are the contributing factors to cast bullet base porosity and what precautions need to be taken to avoid same.

Thanks,
Don

I've noticed lube or grease from the sprue plate causes little half bubbles to form on the base. Usually this works itself out after a while.

A cold sprue plate can cause shrinkage in the base, and insufficient fill-out there.

There's probably more.

-HF

[lwknight]

Lube or oil from the spru plate leeches into the cavity and makes uglie on the bullet base.
Even some wax getting onto the top of the plate can find its way under it.

[Bret4207]

IMO most of the issue comes from inadequate heat in the mould/spue plate area. Running a hot mould with a good sized sprue I rarely get holes.

[x101airborne]

x2 what was said. The only time I have holes in my bases is when I am final warming my mold. usually clears up in a couple of drops. If not, I made a batch of mix with some unknown contaminant in it and it did that hot. I just increased the heat, fluxed, and kept adding 50/50 solder to the mix until it quit. These bullets were sent to the "saturday plinking" bin and I started over with clean metal for my business loads.

[BABore]

IMO most of the issue comes from inadequate heat in the mould/spue plate area. Running a hot mould with a good sized sprue I rarely get holes.

Ditto!

Run the mold hotter, not the alloy. Pour a real healthy sprue. One that almost runs off the blocks if your bottom pouring and one that does if your ladling. Your running a good block/sprue plate temperature when the sprue only builds up about 1/8" or less high. It should take the sprue 3-4 seconds to solidify once your done pouring.

Use something like Bullplate on the underside of the sprue plate. I don't bother trying to coat the block tops. Just get the mold hot, wipe BP on the plate with a Q-tip, then wipe off with a clean paper towel. The first cast or so after applying may show some tiny craters, then it goes away. Try to cut your sprue so you get a slight tearing of the boolit base. It doesn't affect accuracy and keeps the plate hot. A shiny sprue cut is an invitation for trapped air pockets in the boolit's base. I use a small, HS, fan to cool the sprue after it solidifies. Maybe 3-4 seconds then cut and dump. If the blocks run a bit too hot for my rate, I also use the fan to cool the open, empty, blocks for a few seconds before refilling. Every mold runs different, so you must evaluate its performance and adjust your rate and fan times.

[Calamity Jake]

What BA says, only I don't run a fan, instead I run two molds!!!

[44man]

A little tear out is fine. The worst thing is a gas checked boolit when the mold is too cool and you get a lump at the sprue cut.
Sometimes my mold does not have enough time to preheat so I play a propane torch all over the mold and get the plate hot before casting the first boolit.
Hot is goooood!

[winelover]

Yesterday I tried out NOE 432265 mould ( 3 cavity, non HP) which happens to be my first time use of a Aluminum mould. I've always used Iron in the past. Mould prep included cleaning with brake cleaner and was soaked in 375 degree oven and allowed to cool 3-4 times as per NOE's instructions. Turned on the Lee 20 filled with an alloy of 1 Pure lead RCBS ingot to 1 tablespoon (mini-ingot) of 95-5 solder(which I've used before). While pot was heating, mould was heating up on a hot plate. Began casting (applied Bullplate lube) but the bands were rounded for at least 20 cycles. It was only till I increased my tempo to maximum, that fillout was complete. I would cut sprue as soon as it solidified. Worked OK for another 20 cycles or so then I experienced " base-tearing" like I've never seen before. Sprue was crystalizing and causing craters in the base. Cooled alloy down by returning sprues and rejects to pot. (Something I never do with iron moulds) It cools the alloy down so much that the rejects skyrocket even with pot set on maximum. Resumed casting but experienced incomplete fill-out again till alloy temp increased. Bases were better but never perfect. Poured about 300 good boolets that averaged 255.0 + 1 grain for the plain bases and 250.0+ 1 for the gas checked ones. Boolet diameter was .433 -.432 for both types. Guess I need more practice with Aluminum moulds and or try a different alloy. Used what was in the pot from my last casting session. Any recommendations?

Winelover:castmine:

[mold maker]

Getting the mold and sprue plate really hot, and using a fast pace with very little open time, has always worked for me.
I usually start with a really hot melt and reduce it as I settle to a rhythm. Frosted won't hurt, but indicates too hot a melt. Starting this way insures the mold temp stays up until you hit your comfort zone. Big sprue puddle should take 4-6 sec to harden (change from shiny to dull)
That gives the boolit time to draw metal from the liquid sprue as it hardens, and usually provides good fill out and solid bases for me..

[Cherokee]

+1 on what mold maker said

[casterofboolits]

I normally cast with three moulds and place them on top of my RCBS ten kilo pots and let them heat while the alloy is getting up to casting temp. For me, using three moulds allows me to maintain an even temp for the moulds and reduces lead smears by not opening the moulds too soon. I spray a dry film graphite lube on the top of the mould and the bottom of the sprue plate to reduce galling and lead smears.

Lube of any kind that is oily on the sprue plate or top of the mould will cause problems with boolit fill out.

A good hefty sprue will also help the base of the boolit to fill out.

[Bullshop]

Casterofboolits

{Lube of any kind that is oily on the sprue plate or top of the mould will cause problems with boolit fill out.}

Please Sir no offence meant but I must disagree with this statement. There are literally thousands of boards members here myself included using bull plate ( a blend of oils and conditioners) on the sprue plate and mold top and are having absolutely no problems with base fill.
In my opinion your statement is absolutely without merit.
BTW I even use BP applied to a hot mold cavity to aid release and have no issues with poor fill as long as the blocks are adequately vented.

[montana_charlie]

A shiny sprue cut is an invitation for trapped air pockets in the boolit's base.
And that is because...?
CM

[BABore]

And that is because...?
CM

For the reasons I mentioned above. Waiting for the clean cut condition can allow the sprue plate to cool too much. A cool plate allows the sprue to freeze too fast and trap air in the base. Notice I said "can" and is an "invitation to", not it always will. Your an experienced caster and know how to make your molds run right. At least I'm making that assumption. The poster has a specific problem and I mentioned the best methods of solving that. Others seem to agree with that. You may not agree with this, and that's fine. I have proven the method described to my satisfaction with both accuracy tests and weight sorting boolits. I have run my various 400+ gr 458, multicavity molds with +/- 0.1 grain weight variation when I tear a slight sprue. When I wait to make a clean cut, wt. variation goes up. All weighed boolits were also measured on all bands and grooves to eliminate any weight variation being caused by lack of fillout. Weighing boolits is mostly useless unless you also measure. Otherwise you can't tell the difference between air pocket and voids verses poor fillout. But, you already knew all of this.

[44man]

Casterofboolits

{Lube of any kind that is oily on the sprue plate or top of the mould will cause problems with boolit fill out.}

Please Sir no offence meant but I must disagree with this statement. There are literally thousands of boards members here myself included using bull plate ( a blend of oils and conditioners) on the sprue plate and mold top and are having absolutely no problems with base fill.
In my opinion your statement is absolutely without merit.
BTW I even use BP applied to a hot mold cavity to aid release and have no issues with poor fill as long as the blocks are adequately vented.
I agree with this 100%. I have overdone BP with no trouble and look at the guys using Kroil in the mold.

[lwknight]

The OP did say " base pososity" and nothing about poor fill out or voids.
Porosity is mainly caused by a contaminant that is gassing from the heat of molten alloy.
Common spray lubes and wax are the most common culprits.
And where did the suggestion that BP was in this catagory come from?

Talk about thread drift . I don't think many people actually read the OPs' question. It went from the spru plate being too cold ( which does not cause porosity ) to Bullshop defending his product.

[Bullshop]

lwknight
Not so much defending my product as defending the truth. What casterofboolits said simply is not true. When I started out casting there were many non truths being published by the sources we looked to for help. I feel it my duty to not allow any more to get started.

I may be wrong but I think that what is being called base porosity is tearing at the sprue cut. That can make the base look porous. I feel that the whole issue is due to timing the sprue cut. It could be cut sooner or even later and I think that will eliminate the problem of a porous appearance. Think of it like this, if you run a trowel over half cured concrete you get the same appearance of a porous surface.
Lots of things are going to have some effect on this condition like alloy composition, mold temp, alloy temp, time between pour and cut, fit between sprue plate and block top, sharpness of sprue plate cutting edge and maybe a few others.
I think the biggest thing is timing. I cut sprues as soon a they wont wiggle. By that I mean when you cant see any movement of the sprue from the normal tremors in your hand I cut. The sprues are still soft and crumble in my gloved hand and go right back into the casting pot. Maybe not the right way but just one mans way.

[montana_charlie]

A shiny sprue cut is an invitation for trapped air pockets in the boolit's base.
And that is because...?
For the reasons I mentioned above. Waiting for the clean cut condition can allow the sprue plate to cool too much. A cool plate allows the sprue to freeze too fast and trap air in the base.
Then the possibility of air being trapped in the base would occur when the next bullet is poured because then the sprue plate would be too cool...correct?

CM

[lwknight]

It might be my bad and I did ASSUME that any person having knowledge of the term "porosity" is probably has an occupation that has something to do with welding and definately understands porosity.

[casterofboolits]

Casterofboolits

{Lube of any kind that is oily on the sprue plate or top of the mould will cause problems with boolit fill out.}

Please Sir no offence meant but I must disagree with this statement. There are literally thousands of boards members here myself included using bull plate ( a blend of oils and conditioners) on the sprue plate and mold top and are having absolutely no problems with base fill.
In my opinion your statement is absolutely without merit.
BTW I even use BP applied to a hot mold cavity to aid release and have no issues with poor fill as long as the blocks are adequately vented.

Did I some how say something different than posters #2 and #3?

If oil is not a problem when it is in the cavities, why are there so many posts here about how to degrease moulds?

I am not familar with your product, nor was I refering to it in any way.

[Bullshop]

{It might be my bad and I did ASSUME that any person having knowledge of the term "porosity" is probably has an occupation that has something to do with welding and definitely understands porosity}

I dont understand what you mean by that.
I had an idea I knew what the original question was about and tried to give my opinion but I may have been way wrong. I will have to look up the word porosity to see if it means what I thought it meant. Sorry! I am about the worst welder God ever created.
casterofboolits
Your changing horses now. Your origonal post didnt say in the cavities it said on the mold top and sprue plate bottom, correct?

{If oil is not a problem when it is in the cavities, why are there so many posts here about how to degrease moulds?}

As to this question it can be answered in one word, VENTING.

{I am not familar with your product, nor was I refering to it in any way.}

You may not be familiar with our products but you were refering to it when you said any oils. Isnt that what you said, any oils on the sprue plate bottom or mold top? This is all confusing enough for beginners so lets set the record straight.
A good rule to remember about casting is never say never and never say always. When you do there is no way out.

[44man]

I probably started casting sinkers when I was 10 and in 63 years of casting everything with every kind of mold, I never seen what could be called "porosity". It would take some weird metal or contamination.
I also take the question meaning sprue break out.
I wash molds in soap and water and have used all kinds of mold release or none at all and don't see any difference. Some lubes or rust preventatives can gas off when hot but Bull Plate will not.
I have hundreds of molds of all makes and all I have made, all cast the same with no special treatment for any of them. I get the mold hot while the lead melts and the first boolit, even from a new mold, will be perfect and I can dump 20# without a single reject unless I take a break but the torch gets it all going again before I get a bad boolit. It is nothing more then knowing what you did before a problem occurs.
Casting is just too easy and if ONE bad boolit is made, the problem is solved before another is cast.
Maybe it is all the years but I don't understand all the questions and solutions posted. I cast everything from pure lead to hard alloys and never had to add tin for fill out, pure casts wonderful. I add tin to alloy metals ONLY!
I feel many of the old timers and casting experts here get confused about problems posted too. Casting just gets to be second nature with no thought needed.
I do agree with some answers even if I don't understand why there was a problem to start with. I chalk it up to experience and feel sorry for a new caster with a problem but just too many things don't mean a thing.
If you see me boiling a mold or using funny chemicals you will know I fell down the hill! [smilie=l:

[Bullshop]

44man
Well said. The one that makes me scratch my head is "reject rate".
With the possible exception of the first couple casts once your temp and rhythm are set there should be no rejects. If there are rejects then either one or both temp and or rhythm are off assuming the mold is properly vented. In my opinion if any are rejects all are rejects until the timing and temp are right.
There are also two temps to be concerned with, the melt being one and the mold the other. The rhythm or rate or whatever you will call it sets the mold temp. When its right its right for all not just for some. If its wrong its wrong for all not just some.
That's why I say I just dont understand the term "reject rate"
I guess if I try to remember back to the beginning there was a time. Just as you say it seems to happen now without much effort.

[44man]

44man
Well said. The one that makes me scratch my head is "reject rate".
With the possible exception of the first couple casts once your temp and rhythm are set there should be no rejects. If there are rejects then either one or both temp and or rhythm are off assuming the mold is properly vented. In my opinion if any are rejects all are rejects until the timing and temp are right.
There are also two temps to be concerned with, the melt being one and the mold the other. The rhythm or rate or whatever you will call it sets the mold temp. When its right its right for all not just for some. If its wrong its wrong for all not just some.
That's why I say I just dont understand the term "reject rate"
I guess if I try to remember back to the beginning there was a time. Just as you say it seems to happen now without much effort.
Reject rate is a funny term to be sure. The main thing that comes to mind is just how good are the ones that are NOT rejects. Is it only appearance? Or do some have voids? Just how does one get a void?
If I had to throw ANY boolits back in the pot, I would not trust the rest either unless I know for sure what caused a few bad ones. That is the secret, fix it quick before wasting hours and getting 50% of what you think are good boolits.
One mold---EASY, two takes a little heating with the second over the first and three takes a little more juggling to get them all going.

[Don Sarkisian]

Gentlemen,thanks for all the valuable responses.1st let me say that I am 74 years and have cast for a while but always with either Lyman or RCBS steel and iron molds.My new mold is an aluminum one of excellent design from a highly respected mold producer.The "half bubble" base pososity that I experienced during the 1st run with this mold was not at start-up but at various stages during the casting of 200 bullets with Rotometals Lyman #2 alloy.Out of the 200 bullets cast about 30 had the base porosity to one degree or another.Corrective action taken when the issue occured was to reduce alloy temperature and the issue went away.The issue also reappeared when bullet frosting started indicating too hot alloy.What I am confused about is whether I was running the alloy too hot or the mold too hot when this issue popped up.

Best,
Don

[sagacious]

Gentlemen,thanks for all the valuable responses.1st let me say that I am 74 years and have cast for a while but always with either Lyman or RCBS steel and iron molds.My new mold is an aluminum one of excellent design from a highly respected mold producer.The "half bubble" base pososity that I experienced during the 1st run with this mold was not at start-up but at various stages during the casting of 200 bullets with Rotometals Lyman #2 alloy.Out of the 200 bullets cast about 30 had the base porosity to one degree or another.Corrective action taken when the issue occured was to reduce alloy temperature and the issue went away.The issue also reappeared when bullet frosting started indicating too hot alloy.What I am confused about is whether I was running the alloy too hot or the mold too hot when this issue popped up.

Best,
Don
Don,
At the start of the pouring session, when the mold is cooler, the sprue can be cut almost immediately, and you'll not experience the "half-bubble base porosity" (aka: torn sprue cut). As the mold temp increases during the session, one must allow a little more time for the alloy to solidify before cutting, and prevent a torn sprue cut. This diagnosis matches your description above of problem vs temp precisely. Good luck.

[lwknight]

OK , you guys were right, Evidently , there are other (albeit inaccurate ) uses for the term " porosity" .

[Bullshop]

{OK , you guys were right,}

:mrgreen:

[Don Sarkisian]

Sagacious,

Thanks for your reply.I need to inform you that I had absolutely no issues with the sprue cut and all were perfect.The "half bubble" porosity was not at the sprue cut but elsewhere on the base and occurred different times during the casting session.The only variable introduced during the cast was alloy temperature change and mold temperature change.Dropping alloy temperature stopped the issue.

[montana_charlie]

Sagacious,

Thanks for your reply.I need to inform you that I had absolutely no issues with the sprue cut and all were perfect.The "half bubble" porosity was not at the sprue cut but elsewhere on the base and occurred different times during the casting session.
Are you saying there are round pits in the base of your bullets?
CM

[44man]

Are you saying there are round pits in the base of your bullets?
CM
If that is true, it is another problem. Poor venting, pouring lead from too high and not allowing full fill to push out all the air, sprues hardening too fast so the boolit can't suck from them, etc.
It is why I ladle pour and hold the ladle long enough for the boolit to draw from the molten lead in the ladle. I don't depend on the sprue.
I don't believe in pressure pour from a pot full of lead. Things happen too fast with a mold filling fast and air might mix with the lead.
Pour beer down the side of a glass or pour into the center of the glass might be a good description.