I did a little research on wheel weights some time ago.
By and large wheel weights come in two varieties.
You have lead based weights on the one hand and non lead based weights on the other hand.
The non lead weights are very easy to isolate because they do not melt in a lead pot. (zinc based weights) They float to the top with all of the other stuff that comes off of all weights (primarily the steel clips)
So lets talk about the lead weights. My information here comes from a technical manager at what was then (two years ago) the primary supplier of wheel weights in the U.S.
She told me that there is no real reason to use anything in weights but lead. No reason to alloy the lead with other low melt metals. She said that the reason that other metals show up is that it is expensive to get rid of it.
She went on to say that the deliberate addition of metals for minor property enhancement never requires more than about five percent other metals (Tin Antimony, and Bizmuth are the most frequently used.) She estimated that her weights were typically signifiantly above 95% purity (She estimated consistent 97%) because everything in the lead that is not lead is more expensive than the lead and consequently the cost of manufacture goes up. This paragraph seems to contradict the previous paragraph but I did not catch it at the time.
She did add though that many weights are now being imported from China and that she has no idea what the allow of those weights might be.
I made some bullets from wheel weights, weighed them, and then compared the actual weight with the theoretical weight of a sphere of pure lead of the same diameter of the balls I had caste. I can not remember the specific numbers but I do remember that the bullets I cast were within one grain of the theoretical weight. It was a .454 ball with an actual diameter of somewhere around .455 and I think I was looking at a theoretical weight of something like 144 grains.
I do find these bullets to be slightly harder than Hornady bullets. But I have also developed a casting technique which provides me with a bullet that is twice as consistent (in terms of bullet to bullet variation in diameter) as Hornady's. (about one half of one standard deviation for mine in comparison with Hornady's)
I have a bunch of ship ballast which I was told was pure lead but I would bet that the person who told me that did not fully comprehend the definitiion of the word "pure".
The bullets I make from weights are about as hard as those I make from ballast.
If you are going to cast bullets, you might want to assume that they will come out a little harder than a pure lead bullet because it is difficult to ensure that the metal you use is pure. To me, the primary impact is the force required to load the chamber. Load with a press outside of the pistl and this problem goes away.
I have purchased a grand total of two boxes of bullets in 35 years. Both were Hornady's and both had consistency which I could easly match (actually beat)by casting.
My recommendation:
Cast your own bullets and don't be afraid to use wheel weights.