I have cast 340 gr (vintage Win. Express bullet mold), 385 gr, 405 gr flat base, 405 bevel base, 405 HB, and 535 Lyman Postel.
I have shot these in a mixture of vintage & modern lever or SS rifles and all have worked to an "acceptable" hunting accuracy at 100 yrds.
However, the most accurate cast boolit I have ever used in any of my 45-70's is a .452 pistol bullet (250 gr RNFP)...don't sh!t yourself laughing yet because it does work, it requires one more step of powder coating up to a dia of .459 but damn they shoot accurate. The one gun that I have shot them most in was at best a 2" grouper with anything else but now will shoot clover leaf groups at 100 yrds and is a damn fine "gopher gun" out to that range. While I haven't crono'd that round yet I would have no qualms about using it as a deer round. I use the same charge in it as I use in my 405 gr rounds that chrono at 1200 fps or so. The second big difference is in the "felt recoil", compared to the 405's, it recoils maybe even less than my .223, you could easily shoot all day with this load.
You may need to get a "substantially" smaller mold if superb accuracy is your defining goal.