I have had good luck with Wheel Weights, I mix approximately 2lbs of wheel weights with 1lb of Hardball from Midwayusa, BRH tests at 14.5 - 15.0, I have loaded 30-30, 30-06, 300AAC,308. I haven't tried it in the 300WinMag yet, but I'm reasonably sure I will have to Gas Check them in order to prevent Barrel Leading. Be sure to use a cleaning agent in the lead, it will fload the impurities to the top as slag, then just remove it. That leaves the lead bright and shiney. I use a 10# pot, and heat the mold on top as the lead is coming up to temperature. Has the mold hot enough that it cuts down a lot of trial time for good flow thru the mold for good bullets. I let them cool until the next day, then size and if needed, Lube.
Good Luck
Dan