Cast hollow points can work wonderfully but you have to match the hardness to the intended velocity for best results. What works best for me is to decide what velocity I'm going to run them & then cast my slugs to match it.
My normal hunting velocities with 41's, 44's, 45's & my 5 shot 480 is about 1100-1200 fps & I only use cast bullets, either solid or HP's. Here's what works for me.
800 fps I use 50% WW & 50% pure lead
900 fps I use 60% WW & 40% pure lead
1000 fps I use 70/30
1100 fps I use 80/20
1200 fps I use 90/10
& over 1200 fps I use straight WW alloy
The 70/30 mix is my most used alloy, and I also use softnose cast a great deal, actually like them better.
If you have correct bullet fit this works very well, I've use it for 45 years & remember many millions of bullalo were taken with pure lead. Also the old Colt 45 Blackpowder loads were pretty much pure lead, thats a 250 gr. slug at around 900 fps. The government expected these to shoot through an Indian pony.