Buller Comparators (SAC vs. Hornady)

[Yama Arashi]

Simple question on bullet comparator measurements for those with experience. (New rabbit hole for me.)

- Dummy round 6.5x47 - 140gr Berger Hybrid bullet - Lapua Brass

- Using a modified case and the Hornady straight OAL gauge to the lands, the base to ogive measures 2.093 with the Hornady 26 bullet comparator

- Using the new SAC 6.5 bullet comparator, base to ogive on the same round measures 1.984 = a difference of 0.109 shorter compared to the Hornady.
COAL on the dummy is approx 2.80+
.163 freebore on the reamer

(According to SAC - "This 6.5mm bullet insert has a generous start radius at .266 tapering down to .256 at a 1.5 degree angle. This replicates the bore of a 6.5mm barrel and contacts the same exact part of the bullet ogive as a chambered barrel does." )

So understanding (and dismissing) that as long as a particular load is shooting great, there are no function issues, and you have found a great jump node with a particular measurement; my question is, is it possible that the bullet isn't actually jumping the amount that people think/say it is? (Due to the fact the ogive contact at the lands may not be the same as the ogive contact on the comparator)

Or is this an already known fact, and the number is simply relative as a value for setting your seating depth?

 

[canezach]

The number is simply relative. I could use two or three different comparators from the same manufacturer and will likely come up with different measurements. As long as my measurements are done with the same comparator, the measurements are valid and relative to themselves

 

[david8989]

Canezach is spot on. The numbers you receive using either headspace gauges or bullet comparators are 100% relative. When I measure my shoulder bump with my SAC headspace gauges I'm inserting a fired piece of brass and zeroing the caliber. Then re-measuring until I get a - .002 to -.003 bump relative to my original measurement. So your good to go man, that being said, aren't the SAC comparators amazing compared to the Hornady ones? I'm in love with mine.

 

[want2learn]

you might also consider the Forster Datum set.....i've been very pleased with it. It can measure both COAL and COTB.