I will politely disagree with this, unless we are talking about wadcutters and a flat seater. As we can’t over look those other factors and get the data we are looking for.
Most all seaters do not push the bullet in from the very tip and even if they did, I can grab a couple of say SMK’s out of the box and they don’t even have the same OAL.
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So, if I did happen to seat them to the same OAL, they would all be different distances off the lands, .005” different for just those two projectiles. If I measure from the base to a datum along the ogive, I do get the same measurement for both, because it ignores tip inconsistencies.
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So, I go by ogive measurements to see if my seating depth is consistent, not OAL. Caliper mounted attachments make it easy.
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However one could even use the seating stem itself, if they wanted to and it would stilll be more accurate than counting on bullet tips being perfect.
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Will tell you more about seating consistency that an OAL, almost every time.