As others have noted, WW will work in rifles but generally the ball must be smaller in diameter. This is because pure lead is soft and the patch will be depressed into the metal. WW metal is hard and will not deform as readily and makes loading more difficult. On the other hand, WW seems to work well in smoothbores provided you use wads, tow, or just about anything but a patch. Using a patch puts you right back where you are with a rifle, in need of a smaller ball.
I thought I'd make my contribution in regard to wheel weights themselves. It used to be simple. Wheel weights were pretty much wheel weights but that's not true anymore. There has been a move away from using lead and so in a given bucket of used wheel weights you may find some made from almost pure lead, the harder lead alloy we are familiar with, zinc, steel, and even some sort of polymer (plastic). The trick is to separate the lead and alloy weights from the zinc, steel, or poly. It's not that difficult. First off, sort the weights into two piles, stick-on and clip-on. Use a pair of wire cutters or other appropriate tool to check the hardness of the stick-ons. You may find that most are soft lead. The metal will mark easily and the marks will be shiny and silver colored. Set those aside for casting into rifle balls. You can do the same "tool check" with the clip-ons. Remember that the alloy weights will be harder to nick with the tool than pure lead. It's a matter of developing a feel. Zinc and steel are much harder to mark with the tool. It will be pretty evident you aren't dealing with lead or lead alloy. They may also be marked "Z" or "Zn" for zinc or "Fe" for steel. Put these aside in separate buckets. You can sell the metal for scrap. The polymer weights can be thrown away. They have no value.
Just in case anyone is thinking "Why not just put them all in the pot?" there's a good reason. Steel weights will simply float and will not melt at casting temperatures so there is no real danger. But why waste your time? You will have to fish out the very hot steel weights and let them cool safely before they can be disposed of. Zinc on the other hand, melts at about 785 F. That's within casting temps and you will have contaminated your lead. Contrary to what some have told me, once it's melted, it's in there and there's no way to separate it back out. Finally, I'm sure I don't need to tell you why you don't want to toss some polymer weights into the pot. They melt. They smoke, They stink. They get all over everything.
SR51