Measuring bullet bearing surface length

[krw]

I only have 1 bullet comparitor. How do I go about measuring bullet bearing surface length? Wanting diff between .264 123gr Lapua Scenar and sierra MK’s

 

[Bender830]

Without two datums it will be impossible to get a real bearing surface length in a boat tail bullet.
The best you can do with a single is bullet base to ogive.

And even with two hornady comparators a true bearing surface length wont be possible as you have the smidge between the actual bearing surface (which is at a .308x diameter) and where the comparators touch (which is a .300 diameter) to contend with.

To get a real bearing surface measurement youll need a real bearing surface comparator tool

What are you trying to discern with that measurement betwen the two different bullet lines?

 

[918v]

Most people would just approximate using a dial caliper. Are they that close?

 

[krw]

I use 40.5gr 4064 in my 260 w 123 SMK’s. Have some Scenars I want to ld up. If bearing surface is close, i gonna ld 40.5gr to start with on them

 

[RegionRat]

I wouldn't try to over-think the bearing length similitude concept. There are reasons that bullets of identical weights can be different, but bearing length is only one of them.
With what you are about to do, a little load development is a good idea and you already have a good reference point.

 

[918v]

So you have bearing surface, but there is also seating depth and the amount of jump to the lands.