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So I'm about to embark on my first casting session for my .43" Spanish, I have read the Lyman cast bullet handbook cover to cover and various forums but am still unsure of which flux to use.

I was tempted by Marvelflux as it doesn't smoke but after reading about it robbing tin from the pot and causing pot rusting I've decided against it. Some say candle wax and then ignite the smoke but another has recommended saw dust as the ultimate flux and its basically free.
Any strong views one way or another from those who are already casting their own?

Thanks
Mike

I use sawdust if I have it or a wooden stick, has worked for me fine either way its zero cost. You can throw money at cast boolits all you want.....cheap is always cheerful

A decent mold that fits your rifle will outweigh 'owt else.

Dry sawdust from untreated wood is undoubtedly the best, not only does it help remove impurities from the melt but it also helps different metals in the melt re-alloy.

Sawdust as a covering on top of the melt also acts as an air barrier to the surface greatly reducing oxidisation but this is only really practical with a bottom pour pot as it obviously doesn't work so well when dipping.

As I mainly dip and even when using my bottom pours I use a dry stick to flux my alloy, give the melt a good stir and get the stick good and charring. Push the crud on the top to the sides of the pot and start pressing this crud t'ween your stirring spoon and the side of the pot. This will help the metals re-alloy and all you will be left with is a little fine grey powder, this can then be removed. If you just remove the crud from the top then you will be removing metals as well and changing the nature of your alloy. The pressing action with the spoon puts most of it back after a dry wood, stick or sawdust fluxing.

Marvelux is terrible stuff as it gives of a very hygroscopic residue that will rust the hell out of anything metal it lands upon. Fluxes like wax, and grease are really stinky and smokey and do little to help separated metals re-alloy although they will remove some impurities.

The trick is to get your alloy good and clean stirring with a dry stick at the alloying/ingot stage so that all the fluxing you need to do in the actual pot is just re-alloying any wayward or oxidised metal, which sawdust or a dry stick will do admirably.

As a footnote to the above the separation of the alloys, other than oxidisation, only seems to happen at the higher temperatures so good temperature control will avoid this and the layering of the metals, dependant on their density, in the melt which will then need to be refluxed together.

A competent metallurgist would no doubt explain this better and more correctly than I, but what I do is based on my experience, a little reading but metalurigy books tend to be too technical for my knowledge base, and my casting system which works for me in giving very high quality consistent bullets when required.

Glen Fryxell has written extensively on this but even his fine writing gets a bit technical for me with words like eutectic and tertiary seems to have multiple nuances and meanings in the same sentence.

I use Carnuba wax or Rosin, I got given a lump of both. Doesn't take much. The main job of the flux is to break down the surface tension of the liquid so any solids get released to float to the surface. I use bottom pour exclusively and don't skim that much after the first time, if it is on the surface it can stay there.

I've made the mistake of using Marvflux, it is an excellent fluxing agent, but as others have pointed out, anything ferrous will get a heavy coat of rust.

The various metals in an alloy will not normally segregate once mixed as they are in solution. This is the same as the sugar in your tea or the alcohol in your beer is in solution; so no need to keep stirring. The surface of the melt will oxidise more or less straight away after it is disturbed, but this isn't an issue as the layer is only one molecule thick so again it is nothing to worry about and there is nothing you can do about it anyway.

The metals will separate but only when the temperature rises past a given point, there are some nice complicated graphs in the Lyman Cast Bullet handbook that show this. Just make sure the temperature doesn't climb to much and the metals will stay in alloy however and unattended pot without temperature control it is amazing how high the temperature can climb. I use a PID for my temperature control. Dipping is very good at keeping the temperature down on uncontrolled pots.

Dipping by disturbing the surface of the melt can oxidise quiet a lot of the alloy obviously if it is left undisturbed then it doesn't accumulate the same.

Thanks all,

some really good advice here, I think Lyman should drop their chapter on "The Metallurgy of Cast Bullets" and cut and paste the tips given here for a new chapter on "Practical fluxing".

I'm quite looking forward to casting my own, next will be "favourite lubes" I have some SPG but a few tips have landed my way on "Plumbers Tallow" to beeswax from a local beekeeper mixed with good old Lard and Vaseline.

Mike