The illustration below is an extreme example of why COL (OAL, COAL, OL, etc.) isn't the same with different bullets. What you've discovered is normal. If you look at the SAAMI standards
they usually give a fairly generous range for COL, but the purpose for that range is to guarantee fit into and feeding from magazines, and that is all. If your gun is a single shot or if you use your gun as a single shot, the measurements of fit you get are all that matter.
A second point to make, though, is that seating bullets closer to the lands is a strategy for accuracy that each bullet shape seems to like a little different. Read this procedure
from Berger for VLD's (secant ogive bullet shapes). The more common tangent ogive shapes seem to be more forgiving. What's interesting to note, though, is that some bullets in some rifles shoot best when jammed a short way into the lands. Some shoot better a hundredth back of the lands; some three, some five, some eight, some all the way back half a caliber or so. There's no way to know what your bullet will like best in your chamber until you seek it out. Very often you will discover more than one seating depth sweet spot, in which case at least one of them falls inside the SAAMI COL range most of the time, and that's the more versatile one since it lets you use the magazine or not, as you choose for the occasion.