I'm planning to build a 458 hunting rifle. I'm considering using one of the full length ultramag cases and necking it up to 458. There are several existing wildcats based on this concept such as the 450 Howell, 458 African express, and the 450 Vincent Long to name a few. My concern is that using the 404 Jeffrey diameter case and necking it up to 458 doesn't leave much of a shoulder for headspacing. Do any of you have direct experience with this particular type of wildcat or know anyone that has?