Re: Nosler and Sierra loading manuals
There really is no attempt to seat the bullets a specific amount off the lands in most cases when developing a manual. There's so many variables in play for most that this simply isn't practical with most cartridges. There are a few exceptions (the 80 grain SMK in the 223 Rem comes to mind) where the seating is somehow central to the OAL. In those cases, the manual should mention specifically what chamber was used, and some indication of where the ogive was in relation to the lands. Again, in the 80 SMK/223 combination, the chamber was a 5.56mm NATO chamber, which gave an OAL of 2.550"; since most competitive shooters use a Wylde chamber, that bullet will actually engage the rifling at about 2.440", or thereabouts. So there's major differences out there, and a decision has to be made about which one gets used. There's not enough space, time or money to do all the possible variations, and this isn't done in any manual.
A reloading manual is simply a report which states, "We tried this combination of components, and these are the results we obtained. Your mileage may vary." The variation between manuals is simply a very clear demonstration that all those little variables in play can, and do, create some major differences in the final results. That alone, is a worthwhile reason to have a wide variety of manuals on hand, and to update them as new ones come out. Powders change, bullet designs change, throating dimensions in factory rifles change, new components are introduced, to say nothing of new cartridges. Keeping a good variety of manuals at hand is one way to keep pace with some of these changes.
When you set out to load your own, you're doing exactly that; loading your own. If you follow the loads in the manual exactly, you're still not using the "same" components as the manual. It's a different lot of powder, different lot of primers, differen't lot of cases and a different lot of bullets, even if your load is the "same" one listed in the manual. These are the differences we deal with when loading our own. Not to discourage you here, just to let you know where the differences are coming from. Virtually every manual out there cautions you to start with a reduced load an work up to the listed max. It's good advice, and they put it there for a reason.
Anyway, I hope this clears up some of your concerns, or at least sheds some light on how manuals get developed.