Brass Moulds and Cleaning

I was wondering how often do you clean your brass moulds?

I had lead spotting on the faces of 2 of my 9mm moulds, so I decided to clean them.
I disassembled them, coated with Kroil and set inside a glass dish. I waited a week.
I then scrubbed them with a paper towel, that removed some minor spots. I then used a bamboo skewer to scrape at some more spots. I still had some lead that wasn't coming off, it was stuck on the really well, so used a lead remover patch from Birchwood Casey to get it off.

The moulds look good now, but in the process I removed some of the the oxidized brass. Oxidizing is preferred to keep the lead from sticking.

In the past I have ran my lead temps pretty hot, causing the lead to stick to the mould. I think I have that under control now that I have a PID.

What do you think? Opinions? Expert advice?

Never, I clean any buildup as it happens. I had tinning on one mold because I wasn’t proactive in removing it. So any specks get cleaned off as I go. I don’t ever want to have to remove tinned lead from a brass mold ever again.

I clean my moulds the night before Im casting, Ussually a simple hot water dish soap scrubbing is all. I then lube with 2 cycle motor oil. I do wipe the blocks down lightly with the oil very light coat with a q-tip then remove excess with another q-tip starting in the same order done. This givesa very light coat that helps keep lead from sticking. I do this with all my moulds. When new I heat cycle moulds 3-4 times to get the patina started. then cast with them.
While you may have removed some of the patina there should still be some there to help. To fully remove it would take steel wool sand paper or something pretty abrasive. Another help is to occasionally wipe faces with a piece of coarse cotton cloth while still hot this removes alot.

If I have some issues, I'll rub it off with a bamboo skewer or rub it off with a small mini brick of lead. Tinning is a royal pain. I've had to soak with kroil and eventually pick it off.

Having a brass mold that I develop a patina on (by heat cycling) first seems to be the best way to avoid all of that.

I did the heat cycle thing when to moulds were new. This must be some really good brass that doesn't like to tarnish.

Does anyone have pics of some old brass mould that has turned brown?
I have a black powder cylinder flask that is brown from use and lack of cleaning.

Clean the mold Hot, Working Temperature or just above. Sprue lube and/or beeswax on a 6" cotton swab. Use the stick end to dislodge stubborn spots. I laid the halves on my preheat hotplate.

Miha's Brass doesn't tarnish very well. Birchwood Casey Brass Black is the fastest patina I found but it isn't durable. I never got a really deep patina with any of Miha's molds. I'm sure the brass was chosen for machining and heat stability qualities because even Liver of Sulphur has little effect. I came to the conclusion f you want patina start with Bronze.

If you can keep the mold temperature from rising too high after you get the session going, the mold runs cleaner. I'm going to try a temp probe in the next one and see if I can't find the sweet spot.

As far as lead deposits, I have a number of brass molds and I would warn about getting a brass mold hot trying to remove lead deposits as a brass mold can warp! Heating a mold is not necessary to remove lead deposits.

I keep all my molds oiled when in storage, so when I get them out for use I wash with a toothbrush, soap & water, then rinse in acetone to remove any residual oil. When I get a new brass mold I do the same. Any residual oil left in the cavities and you will be dropping bad bullets for quite a while.

A patina on brass is the best protection from lead deposits. You can heat a mold numerous times to develop a patina. I do a shortcut to develop a deep patina by rubbing on a solution of 1 to 1 hydrogen peroxide and white vinegar on the brass with a Q-tip . The solution will turn brass to an aged patina immediately. When I have small deposits of lead on a mold, the solution will dissolve lead. I coat the lead deposit with a Q-tip dipped in the solution, many times this is all that is needed. For more stubborn deposits I dip the eraser end of a #2 pencil in the solution and rub the lead deposit with the wet eraser. The sharp point of the lead pencil will also aid in getting under and dislodging deposits. It may take a little while to remove the deposits, but they can be removed.

Pencil lead rubbed into and coating the bullet cavities is another old trick as the graphite will aid in releasing bullets from any mold.

Brass molds are capable of producing beautiful bullets, but the molds are heavy and they require running hot. I run two molds simultaneously, which gives me maxium production as I am not holding a single mold waiting for the alloy to set and there is much less chance of cutting the sprue prematurely. To get things started, I turn up the heat on the pot until I am getting frosted bullets then back off on the thermostat as needed. After a few sessions you find the sweet spot where everything works and you don't have to fool with it.

I personally prefer a good iron mold since they are lighter, more forgiving and last indefinitely if properly cared for. Brass is my second choice, but to each his own.

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Originally Posted by Dragonheart

I do a shortcut to develop a deep patina by rubbing on a solution of 1 to 1 hydrogen peroxide and white vinegar on the brass with a Q-tip . The solution will turn brass to an aged patina immediately. When I have small deposits of lead on a mold, the solution will dissolve lead.

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This is known as “the dip” and is dangerous when combined w/ lead. It creates lead acetate. It’s what some people use to clean sealed silencers. Disposal of the solution requires taking it to a hazardous waste collection facility. Simply put it’s nasty stuff when combined w/ lead.

I heat cycle all molds, including aluminum, three to four times before using the first time. This is all it’s taken to prevent lead buildup. As you use the molds the patina continues to deepen. Miha’s molds will turn a dark gold cover over time.

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Originally Posted by dragon813gt

This is known as “the dip” and is dangerous when combined w/ lead. It creates lead acetate. It’s what some people use to clean sealed silencers. Disposal of the solution requires taking it to a hazardous waste collection facility. Simply put it’s nasty stuff when combined w/ lead.

I heat cycle all molds, including aluminum, three to four times before using the first time. This is all it’s taken to prevent lead buildup. As you use the molds the patina continues to deepen. Miha’s molds will turn a dark gold cover over time.

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MP Molds are leaded brass so you will produce Lead Acetate even with a new mold.

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Originally Posted by Dragonheart

I would warn about getting a brass mold hot trying to remove lead deposits as a brass mold can warp!

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Nonsense! MP Brass Molds are perfectly stable even slightly above operating temperature. If the alloy is really stuck, heat until the alloy is soft and wipe it off with a cotton swab moistened with beeswax or sprue lube. Best time to clean is during a casting session when the mold gets a little hot. I'll stop and wipe the top and sprue plate, cast a few more and wipe the mold faces.

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Originally Posted by Mal Paso

MP Molds are leaded brass so you will produce Lead Acetate even with a new mold.



Nonsense! MP Brass Molds are perfectly stable even slightly above operating temperature. If the alloy is really stuck, heat until the alloy is soft and wipe it off with a cotton swab moistened with beeswax or sprue lube. Best time to clean is during a casting session when the mold gets a little hot. I'll stop and wipe the top and sprue plate, cast a few more and wipe the mold faces.

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To my knowledge you are correct, the alloy for all brass molds contains lead.

True, brass molds are stable at operating temperature, but how many monitor the mold temperature when heating a mold to remove lead deposits? My point is be aware that brass molds can be damaged by overheating. Just because it hasn't happened to you doesn't make it "Nonsense".

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Originally Posted by Dragonheart

To my knowledge you are correct, the alloy for all brass molds contains lead.

True, brass molds are stable at operating temperature, but how many monitor the mold temperature when heating a mold to remove lead deposits? My point is be aware that brass molds can be damaged by overheating. Just because it hasn't happened to you doesn't make it "Nonsense".

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Back in the Dark Ages before Accurate, MP Molds, NOE and the rest an American entrepreneur tried to make brass molds and they warped due to poor quality brass. The venture died but the rumor persists.

Of course you should try toothpicks first but if the lead is really stuck no amount of Kroil will ever get it off. Vinegar/Peroxide is so slow as to be ineffective as well as poisonous. Lead removing cloth is ABRASIVE. Anything harder than brass has the potential to ruin the mold. It's easy to round the edge of a cavity and all of a sudden there is a mold line where you couldn't see one before.

I used an electric hot plate with a 1/4" steel plate on the coils which is self limiting. It doesn't produce enough heat to get beyond the melt point of lead. At melt point the lead wipes off with a cotton swab, beeswax or sprue lube on the swab will keep it from sticking. I also had tin deposits which have to be cleaned hot.

I agree iron molds are better but not sure why people think they are lighter than brass. A Lyman 429421 4c with handles weighs almost exactly the same as a brass 4c MP 503 with handles whatever slight difference in mass.

You can warp a MP mold. One of the used ones I bought arrived warped. Isn’t warped a lot. But you can see daylight when the mold halves are closed. The gap widens as the mold warms up. Thankfully it still casts fine.

Any mould can warp. Its not so much the material but how hard it was machined and worked. Certain ways of making the stock also contribute to this stress. extruded materials like brass and aluminum have a lot of stress in them heating cooling cycles release this and the material may move when it happens. On a lot of personal tooling we would machine it have it hardened rough grind and let set in the entry way for 4-6 weeks thru temp changes. Sometimes freezing and heating for a week. ( -60* over night then warmed to room temp during the day or shift.

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Originally Posted by dragon813gt

You can warp a MP mold. One of the used ones I bought arrived warped. Isn’t warped a lot. But you can see daylight when the mold halves are closed. The gap widens as the mold warms up. Thankfully it still casts fine.

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Then how do you know it "was warped". It might have been stress relief from milling the blank. I had 1 MP mold with a .001" gap in the middle that also cast fine. I assumed Miha correctly read the "grain".

If anyone has Actually Ruined a mold by heating it please post with Details. So far it's just been an ugly rumor.

Yes, I have a 4 cavity brass NOE mold that was warped. When I got the per-owned mold it appeared to be ok, but two of the cavities dropped finned bullets. First thinking there was a buildup on the faces I thoroughly cleaned the mold, but on closer inspection I could see a hint of light. The mold was in fact warped or maybe distorted would be a better description.

My solution, since I didn't want a two cavity mold, was to put the mold in a machine vice locked down tight and see if even overheating and letting it cool back down under the pressure of the vice would reverse the distortion.

This appeared to work for me as the mold is now useable, but still doesn't drop the almost non-existent mold lines of my other NOE brass molds. The warp could have been due to a problem with the brass alloy, but since the bottom of this mold was quite dark I suspect it was subjected to high or uneven heating or both; either of these can change the crystalline structure of metals. Regardless of how it happened it happened, so it is possible. I suspect there are many molds out there that are dropping bullets with wider mold lines than they did when new and not due to a build up on the mold faces.

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Originally Posted by Mal Paso

Then how do you know it "was warped". It might have been stress relief from milling the blank. I had 1 MP mold with a .001" gap in the middle that also cast fine. I assumed Miha correctly read the "grain".

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I have close to thirty of his molds. You will have to trust me that it’s warped. It’s not a rumor. One can easily ruin a brass mold by overheating it. If they weren’t so expensive I’d record destroying one just because you can.

Did a lot of wear plates in one shop rebuilding equipment these were thin brass and some bronze. Machining improperly as in to heavy or not swapping sides ect ect left a pretzel with visable bows and bends. Heating and cooling the stock before machining relieved a lot of this but then you had warped stock to start with. Heavy machining drilling tapping all induce stress into the parts. Grinding is one of the worse for stress, the shaper is much better since all the heat and work are in the chip instead of the work.

With the new cnc machines speeds and feeds used to cut moulds, the stress in the brass starting out, and the drilling tapping of the holes Itsa wonder more arnt warpping. Heat releases these stresses and the material moves accordingly. a good example is some of the older rifle barrels very accurate if shot slow but if ran to fast every few shots would "move impact " due to barrels walking from internal stresses.

I put the two halves on my hotplate and turn up the heat to maximum. After about 5 minutes you will see/feel that the mold is very hot. I then take a drop of sprue lube on a cotton bud and when it starts to smoke from the mold, then you know the mold temperature is high enough. I then as quickly as possible remove all the tinned spots with sprue lube applied to cotton buds. When completely clean and free of all tinned spots, let it cool down to ambient, this normally takes a few hours. I then scrub it with a toothbrush and denatured alcohol. Then finally I scrub it again in very hot water with dish washing soap.
Then when I cast again, the mold will produce beautifully filled out boolits from the very first cast.
I have several brass molds from MP as well as Accurate, and using this simple method to clean them , I have never warped any of them.
Just want to mention that I got my recipe for cleaning brass molds right here on this very forum, mostly from Mal Paso's previous posts!