There are many fun things about casting your bullets. I just enjoy melting and fluxing the lead.
You can increase velocity with cast bullets in most rounds by water quenching them out of the mold, gas checking the bullet, and then making sure you use a quality bullet lube.
Just remember water quenching has a shelf life though.
The bullets will start softening up over time.
For most shooters this isn't a problem as the normally shoot them right up.
But if it's something that might sit in the box a couple years maybe you might mix some linotype in.
Of course there are also plenty of mixes out there too.
I'ver scored some nice bars of heavy tin/antimony over the years for almost nothing.
But lino gets used most often by me. Just so darn easy to drop a couple pieces in.
For what ity's worth though, if you're gonna do a mix I reccommend you invest in a hardness tool.
I got in trouble a few years back when I added to much lino.
Had a batch of bullets spring back to original size after resizing.
The wouldn't chamber they swoll up so bad.
There's a fix for that also, but I won't go into that.......
Lee makes one, about $50-60 bucks I think. It wouldn't be hard to make your own, if you had samples of known hardness lead to calibrate it with. The Lee model works kinda like a push button ink pen, only with a stronger spring. You put it against the lead, trigger it and a small ball impacts the lead. You then use their scaled magnifier to measure the dimple, and compare the measurement on a chart to obtain the hardness.
A small ball bearing on the end of a steel rod, dropped from a uniform height would do pretty much the same thing. You'd just need to calibrate it on samples of known hardness.