Leade angle and throat diameter

[PJ Hardtack]

I'm having a .510/.511 liner installed in my Erma .54 Gallagher. I've been asked what leade angle I want and what throat diameter - bore or bullet (.512).

Looking in the chambers of my 50-70 Shilohs, I see no throat, the rifling beginning at the end of the chamber. Looks like a pretty abrupt leade angle as well.
In the chambers of my .50 percussion Shilohs, I see an obvious throat of groove diameter that appears to be 3/16ths in length.

I intend to shoot mainly 350 gr bullets that are one grease groove shorter than my Lyman 515141s at 425 grs., same ogive with a larger meplat.

Comments - preferably based on experience .... ?