Stainless steel ?

-- I was wondering why stainless steel is not used to make cast bullet molds ?

You would not want to pay the price that a stainless steel mold would cost you.

At one time nickel was used for molds.

Here is a thread on the subject http://castboolits.gunloads.com/show...l-Bullet-Mould

This was just brought up a few weeks ago. Stainless Steel is harder to machine transfer of heat is low, and weight. It would be an expensive material to machine a mould from. It wold require changes in cutter geometry, speeds and feeds, coolants and possible fixtures and set ups. Cast Iron is inexpensive as a base material, easy to machine, heats fast and evenly, and very long lize. I know of some cast iron moulds on the third persons use. Brass again easy to machine low corrosion, even heat and high transfer. It is a little more expensive material but the speed and ease of machining off sets this somewhat. Aluminum good cost point, easiest to machine it machines at high rpms and feeds with the cheaper HS steel tooling. Aluminum is also the lightest of the materials currently used.

Stainless steel has approximately 3 times the thermal expansion of carbon steel. Not a show stopper, but would have to be figured in.

Thermal Conductivity is the thing that kills stainless steel. It is one fifth that of cast iron, and one twentieth that of aluminum.

Aluminum is really a great material for our purpose. It's only drawback is a slight decrease in absolute durability, which is only an issue if you don't care for the mold.

From what I have read there are lots of negatives and no positives. They'd look neat but otherwise there's no benefit.

I have to wonder how long the stainless would remain "stain-less", after all the heating and cooling.

"stain less" is a misnomer, yes it is a different metal as to steel but not much. The "stainless" comes from a process that seals the surface from oxidizing. You scratch stainless and it will rust. As far as machining the stuff it is more dense and will work harden in a heart beat. At that point stainless needs to be annealed, not an easy process. All this depends on what grade of stainless you are working with.

I gotta wonder how long it would take a sprue to cool in that mold. Aluminum heats fast and also cools fast. Stainless would kill you getting it hot enough not to wrinkle, and then would sit with a sprue puddle for 5 mintues.