06 November 2009
There's not enough info in your message to figure out what your problem is exactly. There can be a million reasons for poor bullets. But since you have raised the issue of drossing let's tackle that. Some things can't be explained in a few words so forgive me if this is a bit long. Some books tell you that regular fluxing is necessary to prevent the tin and antimony from separating and floating to the top. That is untrue because once in solution with lead, both tin and antimony will remain so and can be separated only by sophisticated methods available only to laboratories and foundries.
Fluxing is for cleaning out dirt and dross, that's all. Dirt and dross are not quite the same thing but have the same effect and are removed together so can be discussed together. Dirt is what's on or in the lead before melting. Dross is created by oxidation of the alloy by temperature, mostly the tin, which is why a perfectly clean alloy will accumulate some dross over time.
Oxidation or drossing is temperature related. At 750F it isn't much. Above that it becomes increasingly perceptible until at 900F most of the tin in a 5% tin/lead alloy will dross off in 30 minutes. I have had the experience of a heavy blue/brown flaky dross precipitation from the melt in a Lee 10 lb pot at max setting in 30 minutes. A thermometer showed that to be over 900F which is also in the danger zone for fumes. Drossing is mostly caused by casting too hot. At 600F I can cast continuously for several days before needing to flux.
There is no need for Marvelux or other fancy fluxes that don't do a better job than ordinary candle wax. The foundries don't use them. They use a cheap but effective method called “dry drossing” with sawdust and caustic soda. Don't try it, it can be dangerous and needs experience.
How to recognise when to flux ? Not difficult, the amount of sludge on the top of the melt tells you. Over time the dross builds up until it looks, and feels when stirred, like a thick sludge. A sure way to identify it is to rake off a ladle full, let it partially solidify and dump it on the floor. There's no mistaking the difference between clean alloy and sludgy dross. But that shouldn't be necessary, a little experience will soon tell you when to flux.
You need to vigorously stir a new batch of alloy to make the dirt float to the top, but you don't actually have to flux again after that. You can get rid of dross by simply skimming off the sludge. But that sludge is made up of particles of dross entrapped in the alloy. Fluxing separates them and you save the alloy.
I do it this way. Drop a one inch piece of a cheap candle into the melt and stir it in. You want it to flame. If it doesn't drop in another piece. That usually does the trick. Some books say it is best not to flame, but I found flaming works best. Wear a welding glove to protect your hand from the flames while stirring. It looks like a small but vigorous fire and gives off a lot of smoke. It will burn for four or five minutes, and will leave a pile of fine ash on top of the melt which you skim off.
If the first burn does not produce full separation do it again. If it is done properly the top of the melt should be free of sludge and be clean and shiny.
Give it a try and tell us what happens. If you are still having trouble we can talk about mould preparation, alloy mix, melting temperature etc.