stainless?

why don't mold makers maker molds out of stainless steel? is it cost, or would it wear on the tooling more than regular carbon steel?

Stainless steel is very hard to machine, you'd get a lot of chatter and it might require 2-3 cherries to produce just one mold.

The gun companies had a lot of trouble making firearms out of stainless steel. There were special lubes to over come the galling problems. The first stainless 1911 45 acp did not come from Colt , AMT (Arcadia Machine & Tool) made the first , I got a Hardballer in 1978 and everyone was just amazed at the all stainless construction. Still have it and recently ordered some Madagascar Ebony grips from Ahrends Grips for the old girl, when they come in we going dancing...I bet she's going to look good with her new shoes !
I would think that stainless would be hard to cut but maybe one day a method could be worked out....The gun companies figured out how to work with it.

It does not transfer heat very well . That is why cookware is normally copper layered . Marvin

^ That's what I was about to say. Poor thermal conductivity. Also realize there are many different grades of SS, with greatly differing properties. Some like 416R, often used for barrels, machines well but is not truly rust proof, only rust resistant, and not all that tough compared to say 17-4PH. Some like the 300 series cannot be heat treated but are rust proof. 303 is comparatively gummy to machine. Disclaimer I am no metalurgist just a dude who likes cranking lathe and mill handles.

Stainless has several issues for moulds, heat transfer, machine ability, finishing, and warping. Stainless depending on grade is much more expensive than aluminum, heavier and harder to machine. Stainless can be hard to get chips to break for good chip control. Some grades of stainless Gall easily and more so with heat. Cast Iron (Mehanite), Aluminum in the various grades, and Brass all have good chip control machine easily at higher speeds and feeds, machine to size and finish easily, and have stress relieved stock that's stable and dosnt warp as much. A stainless mould could be made with a cnc edm accurately and easily but I don't know of any makers using one for bullet moulds currently.

I would love to have some stainless ingot molds made from angle or channel. They have no moving parts and heat transfer would bot be a problem. I'm thinking a stainless bullet mold would be problematic for all of the reasons listed above. It would look nice although not very functional.

ok, well, who needs stainless anyways! lol all interesting info... I had a feeling that being difficult to machine was one major reason.

Keep in mind tooling costs are one of the manufacturers biggest concerns. A material that's wears cutters faster, destroys ways wipers and seals faster, produces more cutting force and some other issues simply ups the costs. Throw in the special finishing needs of stainless and the other issues and its doable but not the best. For ingot moulds it would work and be nice looking. Ingots would probably take noticeably longer to cool, but in this instance they may make some really nice looking ingots. Stainless can be welded fairly easily arc with the right rod, mig or best tig. so making these moulds wont be a big issue. You may go thru a few more band saw blades cutting the ends and plates though. I believe I would use 1 1/2 X 1 1/2 or 2 X 2 stainless 8" long of one of the 300 grades. I would cut the ends angled 5* or 10* for easy release. 1/4" x 2" flat stock for the ends again a 300 series and make them 4-5 cavities on each mould. TIG weld them with the appropriate rod and argon gas on the inside forming a nice fine radious in the corners. Now what would be neat is a tapped hole in one side of each cavity for an ID button to be screwed in with a letter number or ID mark for different alloies.

I worked for a major jet engine maker and we used all kinds of exotic stainless alloys. They had to be cut with tungsten carbide,titanium nitride or believe it or not ceramic inserts and special water based coolants. You could get a very nice finish but it was a lot of machine time to get there. Had S&W gone to the aerospace folks they could have showed them insights on how to machine various stainless steels.