OK, here's the skinny on lead alloys as far as I am concerned:
Pure lead will work at the lowest velocities with the gentlest, slowest burning powders. Black powder (which is actually an
explosive) is much gentler on the boolits than smokless, so often, that is the place where you find pure lead being used.
Unless you are paper patching, the alloy does not have enough strength to seal the bore from the gasses and there will be cutting which will cause leading. Also, your boolit will try to strip the riflings witch has pretty much the same effect, unless you have a gas check, but even with a gas check once you strip the riflings, you are pretty much SOL for accuracy.
Here's a picture of a GC boolit that
almost stripped all the riflings:
Attachment 73769
So, you obviously need a little more hardness (at least on the surface of the driving bands) in order to drive a boolit like this. That's where
antimony comes in. Antimony is your hardener. If you drop your boolits from the mold into cold water, it actually hardens them. The thing you have to remember is that they get harder yet over the next 2-3 weeks.
Now, again, look at the previous picture. You see how much is left of that boolit? This is what it started life as:
Attachment 73770
So, its obvious that the boolit also just didn't have any toughness to it. This is where
tin enters into the picture. Tin also adds a small amount of hardness, but its main feature is
toughness. It will allow the boolit to bend and twist, but it will hold together much better.
When you mix tin and antimony together, they will play off eachothers strengths, and act like epoxy inside the boolit. Ie, the whole is greater than the sum of parts.
However, It is very important for accuracy as well as hunting effectiveness, to match the alloy to the application. Having boolits that are too hard will cause gas cutting as well. That's why wine bottles are stopped up with
cork instead of
wood LOL!
You want to play to the alloys strengths and not waste any valuable metal, so use as little antimony and Tin as you can get away with.
I think that an ideal alloy is 50/50 COWW and pure lead, which gives a really rough approximate alloy of 1.5% antimony, 1% tin, 97.5% lead. That alloy will be the cats meow for everything between 800 fps to 1800 fps with the addition of a gas check.
You are correct, COWW are getting very hard to come by, so you might as well start looking for other sources. There are still people that are selling Linotype alloy, and if you buy a couple hundred pounds of that, then all you need to concern yourself with is gathering pure lead (which is still the cheapest metal you can buy BTW), and some solder or tin to toughen the alloy (which is actually very expensive but a very little bit goes a very long way)
I hope this helps.