Seating depth oal guage question

[Colt250]

There may be a simple answer to this or maby I'm overthinking it but it has me stumped for now. Why when using an oal gauge to measure the distance to the lands does the measurement change when measuring using different styles of bullets? I'm using a comparator to get the measurement from the base of the cartridge to the ogive of the bullet. I understand the oal of the cartridge will change according to the bullet profile/weight but if I understand correctly the distance from the base of the shell to the lands/ogive of the bullet should always be the same no matter what bullet is being used.
This is the first rifle I have reloaded for and when I first started I took the measurements using the 55 gr spire points i had at the time. The measurement using the comparator was 2.074. I worked a load for it at .010 off the lands and it did well so I hadn't messed with it since. I am now wanting to try some 53 gr Sierra match kings. With the rifle having an unknown round count I wanted to check it again while I had it on the bench and see if the throat had moved any. I used one of the sierras and checked and it measured 2.127. I was sure with the limited amount of shooting I had done the barrel hadn't gone that far so I rechecked it with the spire points and came up with 2.075. Soo my question is do I completely misunderstand how to use this or is there something I could be doing wrong Any help or explanation would be appreciated

 

[Thump_rrr]

The radius is different with each bullet weight and type.
You will get different distances even if you use 3 Matchkings of different weights.
Eg 55gr, 69gr, and 77gr.

Each bullet weight and type should be treated as a different animal.

Just another thought on this. I have even had some 500 round count boxes of SMK's have slightly different base to ogive lengths within the same box.
I do not find this to be acceptable but I have seen this in the past.

 

[Colt250]

Where are you referring to by radius? I understand the bullet will have a different design and the base to ogive length of the bullets will vary but what I'm concerned with is the base too ogive measurement of the loaded cartridge. I'm using the hornady OAL tool to measure where the lands Are in my rifle which is a measurement that shouldn't change. This is an exaggerated example but even if a 100gr bullets base to ogive measurement was .5" and a 50gr bullets base to ogive measurement was .25", they would still both need to be loaded in the cartridge to the same lengths using the comparator tool to find where the ogive of the bullet is.. The 100 grain would simply be seated deeper into the shell than the 50gr to acquire the same bullet to lands spacing correct?

 

[Colt250]

My understanding is that is why the comparator is used is so that the measurement can be taken at the point on the bullets shoulder where it contacts the lands in the barrel and the over all length of the bullet from the base to the tip becomes somewhat unneeded at that point My problem it that when taking the measurement using different bullets the measurements act like the lands are at different distances. I know this is not the case but don't know if I'm doing something wrong or if I don't fully understAnd the measurement