Casting tricks for brass molds

[Rickf1985]

I have come across a MP 312-159 HP mold that I forgot I even had. It is brand new so I am looking for advice on how to start up with brass molds. I have been casting for 55 years with steel molds and probably 8 years with aluminum. The steel is easy, the aluminum is easy when all the stars align right. Aluminum has to be hot! Hotter than I like to cast at. I was just experimenting today with a steel mold and the same bullet in an aluminum mold and I had to have the temp at 750 for the aluminum. They jumped right out of the mold at that temp but as the temps went down to 700 I started having trouble getting them to drop. At 650 where this alloy likes to run they would stick something terrible. Bullets were formed good with no wrinkles but no drop. The steel mold was dropping them like they were pushed out at 650. And no frosty bullets. I have never used brass so some pointers to get started would be great. And yes, I already knw about getting the mold perfectly clean.

[country gent]

Some like to season the mould by pre heating it several times to get the patina started on it. You do want to pre heat the mould as brass sucks a lot of heat till it gets up to temp. It heats very evenly though out. I lube pins ands hinges with 2 cycle motor oil very lightly. Cast a a brisk pace until the bullets get frosty. then slow down or lower temps. Brass holds heat longer than iron or aluminum.

I would clean the mould with dish soap and water with a soft tooth brush, dry and warm to 350-400 degrees letting cool a couple times. When cool lightly oil pins hinges and top of blocks bottom of sprue plate with a good 2 cycle oil. By lightly a drop or so on one end of a q tip wipe on and then remove excess with the dry end. You dont want to see oil but just the sheen of it.

[Rickf1985]

I can do the preheat, I have an old, really old hot plate. This is one of the ones with the circular burner. I put a piece if 3/16 steel plate on top of the burner to spread out the heat and set my molds on that.

[Wheelguns 1961]

There are alot of good tips and techniques on the MP-molds website. They are definitely worth reading.

[georgerkahn]

I have come across a MP 312-159 HP mold that I forgot I even had. It is brand new so I am looking for advice on how to start up with brass molds. I have been casting for 55 years with steel molds and probably 8 years with aluminum. The steel is easy, the aluminum is easy when all the stars align right. Aluminum has to be hot! Hotter than I like to cast at. I was just experimenting today with a steel mold and the same bullet in an aluminum mold and I had to have the temp at 750 for the aluminum. They jumped right out of the mold at that temp but as the temps went down to 700 I started having trouble getting them to drop. At 650 where this alloy likes to run they would stick something terrible. Bullets were formed good with no wrinkles but no drop. The steel mold was dropping them like they were pushed out at 650. And no frosty bullets. I have never used brass so some pointers to get started would be great. And yes, I already knw about getting the mold perfectly clean.

I'll add a hopeful helpful tip suggested to me a few years back. To wit, I also have a circular -- G.E. brand -- hot plate, and I copied others' idea of an inverted huge tin can with a "doorway" cut into it for the mould atop it. Suggested to me was to pre-heat the mould up-side down! The friend who suggested this had the thoughts that the sprue plate on top, as well as overall top of mould -- that which FIRST gets contact with the melted alloy -- needs to have the least cooling effect on alloy as it is being poured into cavities. Maybe a "better" -- or perhaps just superstitious -- BUT -- this is what I have done since. I reckon, "it can't hurt"
geo

[Rickf1985]

George, I am planning right now to fabricate a square box to do just what you said, A mold oven. I might even control it with a PID since the controls on mine are a bit iffy. I always worry it will go full hot which WILL meld an aluminum mold.

[Rickf1985]

I went to the MP site but all I saw were molds. no information on using them. I will look again.

[Wheelguns 1961]

http://https://www.mp-molds.com/tipsntricks/

If you hit on menu, you get a drop down menu. Click on tips and tricks.

[Mk42gunner]

I've only cast with one brass mold that I can remember, one of those minuscule Italian .58 Minie ball molds. It worked, but man did it get hot. Tiny mold, lots of lead no wonder.

Anyway I don't believe you want the brass part too clean, a bit of patina will help keep from soldering the mold together.

Robert

[white eagle]

to be honest brass happens to be my favorite mold block's, although a bit heavy
I use a clam type sandwich warmer to preheat my molds
and then I just pour until I start getting good boolits for h.p's a bit of pencil lead on the points helps from sticking
brass you can work with the heat from the blocks longer and you don't have to run your pot so hot
aluminum the heat dissipates quickly so you have to keep that in mind but they are nice as well
I also like cast iron but they expensive

[sukivel]

My MP brass molds like to run a lot hotter than my aluminum or steel molds.


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[Wheelguns 1961]

I set my hotplate a little higher when preheating a brass mold, compared to aluminum. I also run the pot a little hotter when doing hp’s. 750 will usually do it, but I have used as hot as 785. Aluminum molds I can usually get away with 725. Small diameter hp’s seem to want more heat.

[Delkal]

I remember reading a warning on one of the bullet mold manufacturers sites that said brass molds can warp if heated too hot. Has anyone else heard this or had any problems?

[Wheelguns 1961]

I remember reading a warning on one of the bullet mold manufacturers sites that said brass molds can warp if heated too hot. Has anyone else heard this or had any problems?

I have seen the warnings. I have never warped a mold. I think that I may have warped a Lee sprue plate once. It was when I first started casting. I can’t remember the details, but I think it was from preheating the mold with the sprue plate down on the hotplate.

[Recycled bullet]

As long as you want excellent bullets gotta cast them hot and fast.

[BJung]

Brass molds need to be heated higher than aluminum molds. Either way, I turn my hotplate at its highest setting and rest my mold block face down on it and the handle standing straight up. Afterwards, I'll take a propane torch and add hit along the steel and brass parts. I'll move to the ingots in my pot and melt the ingots into the pot. Then, I'll turn back to my molds. I think I'm ready in 10-15 minutes, maybe. I also use 2cycle synthetic oil for the pins and sprue plate. I hope this helps.

[Handloader109]

Brass molds need to be heated higher than aluminum molds. Either way, I turn my hotplate at its highest setting and rest my mold block face down on it and the handle standing straight up. Afterwards, I'll take a propane torch and add hit along the steel and brass parts. I'll move to the ingots in my pot and melt the ingots into the pot. Then, I'll turn back to my molds. I think I'm ready in 10-15 minutes, maybe. I also use 2cycle synthetic oil for the pins and sprue plate. I hope this helps.

I would be very careful using a propane torch to heat a mold. Pinpoint heat that comes from a torch will damage the mold. Just don't. Use a hot plate or if you are cheap like me, just do 3 or 4 more casts.

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[Rickf1985]

A hotplate on high is much hotter than molten lead! At least my old circular burner hotplate is. I will melt an aluminum mold, yes I actually did melt an old worn out Lee aluminum mold to see if it would do it.

[JonB_in_Glencoe]

Rick,
I gonna add my 2¢
Casting with different molds, that is, different block designs as well as different block materials, often require different techniques, much like you have stated in the OP in regards to Alum vs Iron.
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For whatever reason Brass molds need more heat. Some brass molds, not all, can develop tinned spots (boolit alloy sticking to the mold) on the block face, near the cavity. It seems that some designs just create hot spots for this tinning to occur. It's a real pain to remove the tinning and it's important to do so, for casting quality. A good patina will discourage this tinning.
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If you have had a mold, like I have, that has tinned, you will read closely to the discussion about getting a patina built up on the mold. Many casters, who have brass molds, haven't experienced this and likely won't. That is why there is conflicting discussion whether heat cycling, or other patina conditioning is necessary.
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If this mold isn't one of the troublesome designs, then if you just start casting, you will likely have no troubles. But if you have some trouble, you'll get a lesson in tinning removal and tricks to develop a patina.

[Wheelguns 1961]

Adding to the excellent post by John B, I have had this tinning before. It is very hard to remove. I flux the tinning, and carefully heat the area with a torch, and wipe with a rag. Repeat until all tinning is gone. It is more difficult than it sounds.