In the case of bullets with a relatively short tangent ogive (which gently curves away from the shank with no abrupt changes), the lands should contact on the ogive very close to the full-diameter shank. With an ogive that begins at an abrupt angle from the shank like a conical or secant ogive, it depends. If the angle is steep enough, the rifling would initially miss the ogive and the initial contact will be on the front of the shank. In other cases, the rifling could actually touch the ogive farther down the throat on the 1.5 degree taper section. It is important to note that I say "initial contact". That initial contact point may be tiny. If you push a bullet hard enough into the lands that you have deformed it enough to easily see the rifling impression, the area of contact may appear much longer and move a little.
BTW, this is why it is often more difficult to tune a load using a bullet with a secant ogive. Berger introduced something called a "Hybrid Ogive" in an attempt to make tuning for accuracy easier.
Chamber drawings can be a little confusing. The groove section will stay at 0.264" diameter and never get smaller. The rest of the tapered throat only affects the rifling. If you actually look at a reamed chamber, the rifling appears to emerge from the grooves, or as Klem stated: "the rifling will start to appear fairly early in the throat".
BTW, this is why it is often more difficult to tune a load using a bullet with a secant ogive. Berger introduced something called a "Hybrid Ogive" in an attempt to make tuning for accuracy easier.
Chamber drawings can be a little confusing. The groove section will stay at 0.264" diameter and never get smaller. The rest of the tapered throat only affects the rifling. If you actually look at a reamed chamber, the rifling appears to emerge from the grooves, or as Klem stated: "the rifling will start to appear fairly early in the throat".