Any info on these, especially parent cases is greatly appreciated. Thanks.

Ken Howell's book lists the .423 van Horn Nitro as being made from the 460 (or 378) Weatherby Magnum case; the 460 v.H. from 460 WbyMag;--both trimmed back-- and the 500 v.H. from the same case but w/ the rim turned off.

There may be other van Horn cartridges--I didn't read the entire book!

the_captn