[killerclowns]

What factors influence bullet seating depth? Do you just roll with a particular distance off the lands, or does this depend on the gun itself or other factors?

[robocop10mm]

In a single shot weapon the only thing that matters is chambering. The bullet can be loaded as long as you want, generally so it just touches the rifling.

In a repeating firearm, the magazine is the limiting factor. The round must not be too long. It must fit the magazine and feed properly. In a lever action repeater, the loading mechanism dictates how long the round can be. These mechanisms generally are fairly picky about OAL.

[FALPhil]

I think you will find a lot of what you are looking for in this article:

Accurate Loads

Also, read the section on seating depth here:

Working Up A Load