I'm using the same mold you are. Straight wheel weights are hard enough to be ok in 45ACP due to the low velocity of the round. I've even cast bullets of plain lead lubed with Liquid Alox that shot just fine and cleaned up just fine. I do not size mine, however I do use a Lee Factory Crimp Die in the final stage. Tin makes the lead flow smooth, antimony is the primary harding alloy. Wheel weights have antimony and linotype contains even more. Some even consider linotype to be too hard by it's self. anyway with 45 you should be OK whatever alloy you use. I've even found that 9mm at 1100 FPS, 30000 PSI do just fine with wheel weight bullets and even 1/2 wheel weight-1/2 lead still works fine with liquid Alox. I did have to quit using my factory crimp die in 9mm. some cases were a little thicker and the factory crimp die squeezed the case back to factory outside dimensions, but the bullet then tumbled from being too small. Switching to a taper crimp solved my 9mm tumbling problem. I talked to the engineer at Lee and he confirmed this sometimes happens. They gave me a refund on my die. Very good customer service. He was the one that told me wheel weights are hard enough, but also suggested I should quench them in cold water. So far it's worked very good for me.
Good Luck!!!