Edit:
Phil . . . If it was anyone but you, I'd just ignore this. But maybe you see something I'm missing. I use to sweat about reloading presses. Then it occurred to me that (1) if the shellholder is in firm contact with the die, (2) that's it. If the shellholder isn't in firm contact with the die, I don't think you'll get repeatable headspacing anyway.
I don't care if the press runs out, flexes, or does the highland fling. All that matters is the shellholder and the die. I suppose some could argue the shellholder needs to be stiff enough to not flex, but for me, I can't see that as an issue. If the shellholder doesn't hit the die, I got a trick from Joel -- epoxy shim stock to the shellholder so it does.
Not that I'll be easy to convince this is wrong, but you're one of the few I'd listen to . . .
This is directed at both Charles and Al, though some parts at one or the other.
First, Charles, I am in full agreement with you. Actually, as you know I make my own dies. Now, I make them long, then grind to length so that they are a perfect fit to the rifle. So, then if the die is left say, .003 long, I can grind the tops of shellholders (that are pretty darn close as a rule) and I can make up various ones to suit cases of different ages, different hardness, etc. On the subject of epoxy with shim stock, I just weld mine up and recut them, or I simply make new ones from scratch. 4140, then heat treat, man, they're a nice shellholder.
No guys, my statement about the press wasn't to imply that they make a hill of beans. I own a Rockchucker that is at work and has been for 10 years. For "Real" reloading, I use a Lee Turret Press. Wonderful thing. Is it true? Hell, I don't know. It might be off by a mile, but my dies are straight so I don't care. No, what I'm saying is, Al, if the press can be off by a mile, wth difference does it make if you indicate the die body? This entire thread is another great example of dreaming up solutions for non-existent problems. Sorta like putting holes in parts to .001 resolution, then welding the parts together. :?
If you WANT to prebore, and want the die straight, then my hats off to ya. I do mine ID and OD in one operation with a boring bar, they're pretty nice. Is it necessary? No. Am I going to chuck it twice just to make it wrong? Well, not likely.
Would someone please tell me what difference it would make if this hole in the die was not centered? How much slop is in the press ram? How much slop in the shellholder? How much flex in the press frame? Is a die that's .002 eccentric going to matter?