Hey Boge,
I have used every type of lead, linotype, wheelweights and many uncertain contents. There is no secret formula for mixing or using casting materials. What is important that you use a consistent mixture.
I have used pure wheelweights for low velocity handgun loads and for magnum loads. I have taken soft lead from meltings of recovered jacketed bullets and mixed it with linotype and wheelweights. They all shoot well and don't harm your gun. I have never worn out a pistol barrel with alloy bullets, but I have tried.
Try mixing your lead (what ever type it is) with 3 pounds to 1 of linotype. I currently use 3 to 1 (WW to Linotype) just to use up several hundred pounds of lino. My wife told me not to leave that stuff laying around after I'm gone. For years, I used wheelweights with 2% tin. The tin doesn't add an appreciable hardness to the bullets, but it does cause the edges, bases and groves to fill out nicely. Tin makes your casting more successful.
Three to one (ww & Lino) will provide great casting for you. We never know what the actual make up of wheelweights are. I keep my different casts separated with dates and mixtures.
My last cast produced 2600 plus inspected keepers over several days of work. I cast 38 special wadcutters, 44 Special 240s and 173 grain rifle bullets from the same pot at the same time by rotating molds. They all work great whether in an old cowboy gun or in a 30-06 rifle.
I have a big cast iron bean pot and a burner in which I melt down the wheelweights and pour it into 1 pound ingots. I keep the pot half full in hopes that the mix will be of similar makings. I cast my lino into 1 pound ingots too. That makes the scientific calculations very simple. My cast bullets don't know that they don't have much class, but they shoot great.
If I were going to be shooting a black powder cartridge rifle, I would use pure lead and tin in a 20 to 1 mix (1 tin) and maybe even a 30 to 1. I have tried my harder cast bullets in a 45/70 Springfield Trapdoor rifle with 24 grains of 2400 and they shoot just fine too.
The bottom line is that there is no magic about all this, just keep doing it.
Harold Clark