To the OP:

Not a very good way to get a measurement. Here's why:

1) The lands may be cutting the bullet slightly as you're using them to seat the bullet, so you might actually be "jamming" a couple thousandths. The bearing surface in the neck pressing the bullet into the lands is much greater than the bearing surface of the lands pushing the bullet back into the case, so it's pretty reasonable to expect that you're getting some "jam" when you perform the test this way.

2) Equally, when you jam a bullet, you run the risk of the rifling pulling the bullet slightly as you remove the round. Target shooters often live by the mantra that if a bullet is loaded, it gets fired - that's often because they'll use a minimal neck tension and no crimp, with the bullet jammed into the lands. Open the bolt and you better have the muzzle pointed upward, otherwise you'll be pouring powder in your action or across the bench. And of course, they'll need a range rod to tap the slightly stuck bullet out of the lands.

3) There are time proven methods for determining COAL, and there are even "modern" methods for using expensive tools to measure it. No reason to use a less than ideal test method.

I'd be interested to see what happens - crimp the bullets at that COAL, then mark the ogive with a magic marker and run them through the rifle. I'd venture there will be a bit of a "kiss" in the magic marker line from the lands.