Ceramic Bullet Moulds

[bowfin]

I have heard of people machining bullet molds out of graphite.

[uscra112]

Have worked a lot with alumina ceramic as used for structural elements of high-precision measuring machines. (You come in contact with alumina ceramic every time you handle a spark plug.)

In the sense of the split permanent molds we use, ceramic would be a poor material. It has a very low rate of heat transfer, so it would take far too long for the poured boolit to solidify. The more you cast, the worse that would get. Getting good castings is all about extracting the heat of the molten metal so that it solidifies into a uniform mass that fills the mold. Slowly enough that bubbles can escape, and so the wrinkles that iron founders used to call "cold shuts" don't form, but quickly enough to get a decent rate of production. Ceramics would fail on the second count.

Ceramic is extremely stable dimensionally, however, and because it is a friable material it can be machined and lapped to incredibly small tolerances. We could get bars six or eight feet long that were lapped straight, flat, square and parallel to a few microns - one micron being 40 millionths of an inch. Interestingly, one of our suppliers was Coors. Alumina ceramic is a prime material for glass-making machinery, and they use a lot of glass.

My experience with "castable ceramics" is quite limited, but from what I do know they are not very strong.

[theperfessor]

Well, I hope I didn't come across as being down on the idea. My background includes a certain amount of product development work. I know that there are a lot of processes, and a lot of materials, that can be used to make a product. And I have no doubt that a ceramic mold can be made for bullet casting. In other words, it is technically feasible.

But my gut feeling tells me that with the ceramic fabrication techniques available right now, the cost of making a ceramic mold, either singly or in volume, is still going to be much higher than an aluminum, brass, or ferrous mold. I don't see the technical advantages making up for the price difference, and I see some technical shortcoming with ceramics that would have to be considered also.

Is this any reason not to try it or talk about it? Not at all! Because somebody may well come up with a material and/or fabrication technique that would change the calculus of the situation enough to make it financially justifiable.

As a manufacturing guy it's just my way of looking at things.

[tonyjones]

theperfessor,

I come to this forum to learn. I contribute where I can but so far I've gained far more than I've given. There are myriad personalities and knowledge levels among the members here. That said, I was hoping that you would jump in here.

Regards,

Tony

[theperfessor]

Let me throw this out as a factor that could change the "calculus of the situation". If we ever have to start casting out of zinc instead of lead a mold material that can withstand the higher temperatures needed would make ceramic molds a more economically viable proposition.

There are also some newer ceramic fabrication techniques that show some promise in reducing cost and increasing production rate that might also tilt things a little more in favor of ceramics.

Ceramics as a material family include a lot of different materials, from tungsten carbide to various glasses and carbon products. Some are so hard they can only be machined by grinding with diamond tools, others are friable enough to be machined with carbide tooling. They also vary in toughness and shock absorbing ability.

Right now there just aren't any ceramics that combine all the properties needed to make competitively priced bullet molds. Which is no reason to not think about them; it is instead a good reason to do research that would deal with the problems ceramics have in this type of application in order to improve the materials and processes used to make them.

In order to improve something a frank appraisal of the problems that currently exist is always the first step of the process. This is not a negative mindset, it's an intellectually honest assessment. Then the problems can be systematically dealt with.

[Centaur 1]

Perfessor, I was thinking about carbide, then you mentioned it. I bet a modular molding system would work. It could use a brass or steel mold body that has pockets machined that will accept carbide inserts that have the boolit shape molded into them. You could have a mold body with 3 or 4 pockets machined in, and you could put in any combination of inserts for whatever boolits you needed that day. Just think of the possibilities if one of the major mold manufacturers teamed up with a company like Kennametals for the carbide inserts.

[TRX]

I was thinking more along the line of making a steel "bullet" on a mandrel, then using it to impress two blocks of pottery clay, similar to a cherry between two metal blocks. Separate the clay blocks, fire in a kiln.

You might need a threaded insert to hole the sprue cutter, and you might want to machine the top flat before firing.

What I was thinking of, was that this would avoid having to make and use a cherry, or use a CNC lathe with boring bar. All you'd need is a lathe to make the mandrel, basically.

Even if the pottery mold didn't last long, it would let you experiment with bullet shapes, grease grooves, etc. for a very low price, and you could have one of the custom mold makers duplicate your successful shapes in a metal mold.

[runfiverun]

i worked in electro-ceramics for a few years their process might prove out better than the full machining route.
lead [and other oxide powders and binders] oxide powders are mixed wet and spray dried, this is then compressed into shape and then kilned.
[a cherry could be inserted and pressed into the initial part] the two halves would be cut apart, and then a machining is done on the part for final cavity sizing and for the handles.
consistant materials and cnc machining would produce final, repeatable, and mixable halves.

[turbo1889]

This post deleted by original poster.



I am in process of deleting everything I have ever posted about casting with zinc because I have decided I will not share any of the knowledge I have learned over the years about casting with zinc due to the bloodthirsty prejudiced posts of some members on this forum viciously attacking those who cast with zinc. I will not share my knowledge with the enemy.

[a.squibload]

Even so, it sounds better than whittlin' boolits out of ingots.

Anybody got a band-aid?

[Cap'n Morgan]

Ceramics has a low thermal conductivity, which is one of the reasons they work well for investment casting molted steel. The steel must stay molten long enough to ensure a proper fill-out. For the very same reason I think ceramics would be a poor choice for a boolit mold - The cooling period would be too long.

[runfiverun]

if there were inserts of aluminum or steel, the heat migration would be greatly increased.

[Suo Gan]

Not trying to make fun, but what is wrong with aluminum, cast iron, or brass? Easy to machine, easy to use, not that expensive. This is reinventing the wheel to me. I have some ceramic balls that my dad used to fire rockets into at the test site. You can see where they took a direct impact and are still in one piece. Ceramics are amazing, but I don't think this is the right set of circumstances to deserve much noggin time. To me at least. If the argument is for shooting zinc bullets, which has some merit I grant that, mainly because they do not need lube. But zinc alloys have always run several times the price of lead alloys. I have been selling my zinc wheel weights. I have even traded them one pound of zinc for three pounds of lead.

Anyway, best of luck, certainly hope we will not have to be shooting zinc anytime in the near future myself.

[uscra112]

Gee, maybe there's a use for my boxful of wornout AMAL carburettor bodies after all.

[Southron Sanders]

Brass Moulds are much superior to Aluminum Moulds-but Aluminum moulds dominate the market. WHY? Because Aluminum is so much cheaper than brass.

Unless ceramic materials fall to the price of aluminum or lower, I don't see any future for ceramic moulds rather than for custom moulds where the customer is willing to spend a lot money for such a unique mould.

It always goes back to economics-just like about everything else in life.

[Echo]

It's outside of my skill set, but it seems to me that the ceramic wouldn't absorb the heat from the alloy very fast - so the boolit wouldn't set (freeze?) very fast. ???

[garym1a2]

Try BeO ceramic (Berilum Oxide), it has very high thermal conductivity. Very expensive material.

[Willbird]

I have heard of people machining bullet molds out of graphite.

I have always wanted to try making one from EDM graphite.

[Blacksmith]

I have some experiance in Lost Wax casting and the manufacture of ceramic reinforced metals.

The raw material cost of Machinable Ceramics are not cost effective when compared to conventional mold materials. Unless there is an offsetting advantage in properties aluminum, brass and steel are cheaper. Here is a source of four types for you experimenters:
http://www.mcmaster.com/#machinable-ceramics/=ehc1lv

Lost wax would work but with a higher production cost because of more steps and more consumables. The one niche Lost Wax would be good at would be for testing designs. The jewelry industry uses valcanized rubber or silicone rubber molds for making wax patterns. You could machine a metal pattern Boolit, make a rubber mold inject wax patterns one at a time then assemble many patterns on a wax sprue tree and invest (coat with ceramic) that then burn out the wax and cast a few dozen or few hundred for testing. If the design worked go ahead and have it machined in a metal mould.

Pottery molds would also work but the down side is some pottery ceramics shrink quite a bit in firing. Boolits may be too small to matter but you would have to watch that and maybe oversize the pattern.

Back in the black powder days some round ball moulds were made from slate or soap stone. Jewelers have cast silver and gold in Tulfa (a volcanic pummice), Cuttlefish Bone, and sand moulds. Another casting process that would work is Spin Casting in rubber molds, widely used with lead and zinc alloys, here is a link to one equipment manufactor:
http://www.conquestind.com/spin_samples.php

Blacksmith

[Willbird]

There is also lost foam to consider. The molten metal in some cases burns out the foam, not so sure about that for bullets. I know they use lost foam for sand castings, not sure about investment castings. The castings from lost foam sand castings are awe inspiring in their detail. The stuff we worked with used styrene bead type foam, not sure if you can use a closed cell foam or not. One thing about those metal parts however, they can be a bear to machine because they have a thin layer of the ceramic on them...and one time they tried recasting the chips from the process, and the result was a casting that ate every PCD(poly crystalline diamond) tool in the process within 10 parts...maybe not good going down a rifle barrel .

Bullets are usually cast in what would be called permanent molds...one benefit is that they are more consistent, a lost wax part is a casting from a mold that is usually made from a casting from a permanent mold...one more layer of process. One interesting possibility however is to make the mold for the wax part, on a 3d "printer" that will assemble a plastic part from a computer program.