Bullet Seating Troubles with Microjust

[JustMe2]

While the term "ogive" is often used to describe the particular point on the bullet where the curve reaches full bullet diameter, in fact the "ogive" properly refers to the entire curve of the bullet from the tip to the full-diameter straight section — the shank.

So, your seating stem and your CBTO Comparitor are hitting your ogive at 2 different points on the ogive. The seating die contacts just below the tip of the ogive and the comparator contacts closer to the end of the ogive. That is most likely where your inconsistencies originate. Consequently: 1) maybe the stem is contacting the plastic tip, 2) maybe the bullet ogive angle is not consistent for each bullet, so the 2 contact points are changing from bullet to bullet, 3) maybe your primer is not flush and contacting your caliper, 4) maybe your brass base is not flat, 5) etc.

 

[Mikecr]

There are common misunderstandings in this field that build miscommunications.
It's amazing to me that so many manufacturers & experts fail to get the terms in their own specialties correct..
Things like caliber/cartridge/bullet, interference/tension, ogive/contact datum, bore/groove, MOA/IPHY, concentricity/runout, etc.

 

[crkckr]

There are some definite differences in bullet to bullet OAL and BTO. I suspect bullets being made on different presses but I've no way to confirm that. Unless you can somehow buy bullets made on just a single machine, there are going to be subtle differences, which can lead to differences in your COAL, no matter how you measure it! Personally, I think bullet run out is more likely to contribute to larger groups than a bit of seating depth difference but I can't even confirm that, it's just my intuition, which is probably not something to rely on if you're shooting benchrest. I'm sure someone, somewhere along the way has done some research on the matter.
Cheers,
crkckr