Hello All,
I had a lot of trouble finding info on alloying pure antimony with pure lead so I thought I'd share what I did. There's plenty of info on this site and others but it all gave me the impression that it was extremely difficult. It was extremely simple and easy and there's no need to spend a fortune for pre-mixed stuff.
Most of the boolit metal I have accumulated is pure soft lead. Where I live (Florida), it is fairly plentiful if you patiently watch craigslist and drive a bit. Lots of boat ballast, diving weights, and other types of ballast from scrapped machinery. Anywho, I have around 500 pounds of it at this point and my stash of wheel weights is getting low so I bought 5 pounds of pure elemental antimony on eBay. (It is really pretty, sparkly stuff!!) I am lucky to have a source of free tin (they save the dross for me from a lead-free wave-solder machine at work so I get probably 20-40 pounds per year). However, you can also get some the way I used to collect it by scrounging thrift shops and buying pewter.
I wanted an alloy of 93% lead, 3.5% tin, and 3.5% antimony. Although some might consider this too soft, I Powder Coat my bullets so it's not as important. I plan to use these mostly for 9mm & .380 to start with. I'm sure this method would work fine for other ratios.
When I clean and pour my lead, I use mini-muffin tins as ingot molds in order to have some small ingots to get exact weights for mixing alloys. I weighed 9.3 pounds of my pure lead ingots. Then I weighed 0.35 pounds of tin and chose pieces of antimony to weigh 0.35 pounds. Then I used a Lee 20 pound pot (I bought an extra pot specifically for mixing alloys because I don't want to dirty my nice Lyman 25 Mag furnace and foul it's spout by emptying it completely).
I melted the pure lead first with the pot set about 5. Then I put in the tin and let it melt. You MUST put in the tin first as it helps the antimony to dissolve. Then I fluxed with sawdust. I have regular flux but I DON'T use that (mine is Frankford, similar to Marvelux) I don't use it because I read that your alloy metals preferentially oxidize faster/more than lead, so you are removing some of your hardness metals when you use it. I bought a spring-loaded stainless steel mesh ball for making loose-leaf tea as well as a small stainless steel kitchen sieve. I bent the handle on the sieve to 90 degrees.
I first put a piece of antimony in the stainless mesh ball and SUBMERGED it in the lead. I moved it around under the surface a while and it started to melt nicely. It was taking a few minutes, so I grabbed a pair of all-metal vice grips (no rubber handles) and GENTLY clamped the ball handle to the top sides of the pot and gave it 5 minutes or so. It melted perfectly. The ball was too small, so I next put all the rest of the antimony in the pot and used the sieve with the handle at 90 degrees to submerge it and again clamped it to the side with the vise grips to hold it under. Another 5 minutes and it was all melted nicely.
Then I fluxed a few times and commenced pouring my new alloy into ingots. After fluxing with the sawdust again, there was almost no junk on the top to skim.
Please note that there are crucial safety considerations here that I don't want to take the responsibility to address. You need to look up health and other risks of antimony (serious) and take appropriate steps to protect yourself.
I hope this helps someone, and I'm glad to answer questions if I can!