Usually leading is a fit problem, not a hardness problem. I never had any luck with store bought boolits unless they are LBT from good companies like Cast Precision, Double Tap, or a few others.
I had samples from Laser Cast and did not like them at all. Poor accuracy and leaded bores. Seems as if all are too small and I don't like the alloy.
Bulk boolits are just no good.
I shoot nothing but cast and some of my revolvers go two years without cleaning the bore, there is no leading. I clean the cylinder pin and hole often to put clean STP on it and the ratchet.
I have found soft PB boolits do not group and have tried 50-50 WW's and pure. If I use a GC and oven harden them, they are more accurate yet expand great. As I get harder accuracy increases but I have found no use to go harder then Water dropped WW metal although adding a bit of antimony and tin can increase accuracy.
Hard boolits with a good meplat work just fine on deer from the .44, .475 and .500 JRH at 1300 to 1350 fps. OK in the .45 Colt at 1160 fps. Much slower or faster and some expansion is needed. Smaller calibers need some expansion.
My problem has been the 45-70 BFR at 1632 fps with hard. It is a hole punch and goes through deer so fast the lungs are intact with just a hole. Some have gone over 200 yards with poor blood trails. I went to a 50-50 HP at 420 gr on one and blew up an entire shoulder on exit so it was too soft. I am thinking 75-25 might work.
I make most of my own molds and none of my guns get leaded. Accuracy is actually better then a lot of jacketed.
The revolver can not be super tight, some cylinder play is needed. The Keith design has never shot as good as I want, poor guidance through the forcing cone.
I have all kinds of molds. Ranch Dog has good ones and there are a few good Lee molds. Many fine custom molds and even a few good Lyman molds.
I use Felix lube and in the .44 and .45 I use a Fed 150 primer. I only go to the 155 starting with the .475. That is with all powders even 296 and H110.
This is what cast can do. A 50 yard group with a BFR .500 JRH.

Then 5 shots at 50 yards with my Vaquero using the Lyman 452651.

This is my old .44 SBH with the RD boolit. I shot the group at 50 and the can at 100 yards. I hit the rail with one so I aimed higher for the last shot. Don't give up on cast.