Try the Lee C476-400-RF boolit, it is amazingly accurate and also shoots great with 15 gr of HS-6.
I use 26.5 gr of 296 for hunting with it.
I can not get the accuracy I want with ANY Keith design boolit in ANY of my revolvers, never could with all the guns I have owned. Fooled with the blamed things for 58 years and all they do is shoot decent, never great. I don't think they have the right guidance at the forcing cone. A revolver has to be better then perfect with them.
I use the RCBS 245 SWC for plinking to save lead with my .44 using 7 to 10 gr of Unique and finally have it shooting better but it does not match any other boolit. After a lot of testing I found the boolit shoots better and better the harder I make it. It has to be 28 to 30 BHN before it groups at 25 yards but still spreads a little too much at 50.
I have had no luck with any in the .475 at all.
The Keith was used with soft lead in Elmer's day but let me show you what happens to it in the gun.
Nuts, I can't, Photobucket is under maintenance.
Anyway, a soft Keith turns into a truncated cone when slammed with pressure but slump can be uneven. Why not start with a better shape instead of making the gun change the shape?
Another hint for you. The faster the powder you use, the harder the boolit must be because all the pressure is applied to the lead RIGHT NOW. Even a .38 special with those soft wad cutters will expand the boolit to full forcing cone diameter and squirt lead from the gap. I have seen too many of them with leading on the outside of the gun along with rifling filled fully up with lead.