I just loaded my first batch of .458 Lott ammo utilizing new Hornady brass. Although this is not the first time I have ever loaded a caliber with a seperate case-mouth expander (my 404 Jeffery dies are three-piece), this is the first time I have loaded what I would consider a straight-walled case.

Apparently, I did not go deep enough with the expander ball, because when I seated the bullet, there is a bulge where the bullet base stops. I'm not worried about it, since all rounds chamber without problem and I'm sure the cases will fire-form just fine when I shoot them, but I'm wondering, if I had run the expander deeper, would this problem have been avoided? With my 404, I just barely run the ball deep enough in the case to easily start a bullet. None of my reloading manuals cover how deep to run the expander or exactly when in the process case-mouth expansion should take place.

Do I need to run the expander ball deeper in the straight-walled .458?

The bulge is proof you have tight "neck" tension on the bullet.The thicker the case wall the more pronounced the bulde. The bullet base shoves the case wall out as it is seated and further belling of the case won`t help.

Don't worry about the bulge, enjoy!
Good luck!