Bearing surface comparing

[odoylerules]

I am trying to take things to the next level. I'm starting to research reliable ways to compare bullet bearing surfaces. When I use 2 comparators locked onto my calibers, I get inconsistent readings depending on thumb pressure. I've tried over and over to find a repeatable method but I can get variances of 1-2 thousandths on the same bullet.
For those that do this or believe in it how do you accomplish it reliably? Is it worth my time? Also how many of you sort bullets by weight?

 

[dok7mm]

Bearing surface is a fairly consistent measurement compared bto and ogive to meplat measurements. The latter two measurements are more important, in my opinion.

Your current method is alright for comparison, but will not give you true bearing surface unless your comparator holes are both .001" under caliber.

I use a variety of stands equipped with high quality comparators. To check bearing surface, I attach one to stem on a digital dial and seat the bullet into the base comparator. The spring in the dial will hold a consistent pressure on bullet for consistent readings. It is important to keep comparator holes clean, along with clean bullets.

I test 10-15 bullets, zero the dial on mean length and start measuring. I always keep several of mean/zero length aside to check for dial drift.

The tool that will make a difference on target is the Bob Greene comparator for finding ogive profile consistency.

 

[odoylerules]

I just measured the bearing surface from two different lot# of Berger 215 Hybrids. There's .020" difference! That's gotta have a big effect

 

[dok7mm]

I have never seen that. Not saying it's not possible. I have 2600 of same lot #, having used 400. My BTO measurement was +/- .0015" (.003" sorted in 3 groups) with 13 outliers of .004-.007". That includes boatail and bearing surface. Guess I just got a good lot.

Two lot numbers, coming off different dies would show a variance, no doubt, but .020" is a lot on bearing surface. Definitely wouldn't shoot to same POI.

 

[jasent]

I have seen that kind of variance before with Berger not not often. Also check a few nosler, Hornady, Sierra, ect. I've seen those >.05" variation in the same box!

 

[Timeout]

I have not experienced that kind of variance with Bergers of the same lot #. I think Berger would be very interested in examining those bullets. Contact them and see what they say. I'm strictly guessing, but expect that they would pay the shipping to look those over. Berger bullets are known for consistency. I find them to be the closest to custom bullets with regards to consistency. Some other brands, not so much. If Berger will take a look at the ones that you have, please report back with the findings.
I stand corrected as lot to lot, you can find considerable difference in the bullets.

 

[Timeout]

Lot to lot, bullets will vary considerably. Within the same lot #, I find Bergers to be very consistent.

 

[Greyfox]

Lot to lot, bullets will vary considerably. Within the same lot #, I find Bergers to be very consistent.

I have also found this to be the case with several of my different loads. It's also the case with Sierra Match Kings. While I may have had to adjust my seating depth, and have experienced minor velocity differences, I have generally been able to match my original performance. When possible, I always attempt to buy sufficient same lot quantities. I just acquired 2/500ct boxes of same lot Bergers which should be just enough to get through the remaining barrel life on my PRS rifle. They did require some "tweaking" to duplicate my original performance. IMO, lot to lot bullet consistency amongst the manufacturers is surely one of the weak links in precision shooting.

 

[odoylerules]

Just to clarify...within the same lot the variance in bearing surface is about .003
From one lot to another of same 215 Hybrids I've found difference of over .021"

 

[Pdvdh]

Just to clarify...within the same lot the variance in bearing surface is about .003
From one lot to another of same 215 Hybrids I've found difference of over .021"

No surprises there...

 

[odoylerules]

No surprises there...

It sure was to me. I'm relatively new at precision long range reloading

 

[wboregon]

I feel like CNC mono metal bullets might solve a lot of these issues.

EDIT: not saying I want to pay the prices for them, although once your into 338 bullets, 1 buck a pop doesn't seem like the end of the world.