Bullet lengths, from base to tip, are rarily completely consistant. I've measured Hornade V-Max and SST bullets and seen as much a +/- .003" variation, but the accuracy is still very good. I've found Nosler BT's are much more consistant than the Hornadys.

When the load manual says the COL should be X, as long as you're not too much shorter or longer than that number you should be just fine. You don't want to be too much shorter because you could have pressure problems, but you can seat them out longer as long as the bullets don't hit the lands and you work up like you should you should be fine. If you want to have really accurate and repeatable measurements, you need to measure the bullet off the ogive not the tip. Stoney Point makes a set of bullet comparators that clamp onto your dial/digital caliper and do just this. This really helps a lot if you're playing with seating depth to find an accurate load. I stopped worrying about base to tip COL beyond ensuring that they aren't too way too deep or way too shallow. What I do is measure a number of loaded rounds and average the measurements, and as long as the average isn't below the stated COL in the book, and no one cartridge is more than .003" shorter that the recommended COL, I call it good. I also like my loads to fit in the magazine, so I test fit them there too. Then I measure them with my comparator and write down the measurement, which seldom varies more than .001". I then use this measurement to set and adjust my seating die in the future.

Mike