Should Bullet Base to O-Give measurements be the same?

[AznTactical]

I've just started to reload 6.5 creedmoor tbd distance off the lands and am very new to this. Shouldn't a bullet's base to O-give measurement be the same when using bullet comparators from Hornady and Sinclair? I started using Hornady's aluminum comparator until my Sinclair stainless comparator was finally in. The Hornady measured a consistent .053" longer than the Sinclair.

Bullet base to O-give examples that I've measured:

Hornady ELD-M 147gr:
-Sinclair Bullet Comparator 0.743"
-Hornady Comparator 0.796"

Hornady ELD-M 140gr:
-Sinclair Bullet Comparator 0.711"
-Hornady Comparator 0.764"

Hornady ELD-M 123gr:
-Sinclair Bullet Comparator 0.611"
-Hornady Comparator 0.664"

 

[Olen_4504]

the two different comparators are obviously measuring off two different points.

which doesn't matter as long as you use one consistently.

 

[lash]

As mentioned, the comparators are most likely not measuring at actual ogive point. They are just measuring at a specific diameter point on the bullet. That’s why they are called comparators and not ogive measuring devices (OMD). They provide comparative measurements from one bullet to the next.

 

[AznTactical]

But doesn't a comparator insert "replicate" your chamber's throat and measure the bearing surface of the bullet which that dimension drives me to load my roads to BTO?

 

[whatsupdoc]

But doesn't a comparator insert "replicate" your chamber's throat and measure the bearing surface of the bullet which that dimension drives me to load my roads to BTO?

No it does not replicate the throat.
The comparator's provide you only with a reference measurement, as mentioned above it does not provide a exact ogive measurement
You use that reference measurement to confirm/adjust the bullet to lands measurement.

So if you use the hornady OAL tool to measure the case base to the lands for a particular bullet and you measure 2.185 using the sinclair tool (2.185 is your reference measurement).
You would use the same sinclair tool when seating bullets and set the die to seat the bullets to 2.165 giving you a .020 jump to the lands.

 

[lash]

No, no usually nor necessarily. It compares the measurement of one bullet or loaded round to others. Your simplest answer is right on your bench. Measure the inside diameter of each of the two different comparators that you have.

Now, to make things even more interesting, try and get a measurement of the ID of your seating die insert where it contacts your bullets. You probably will not have the ability to do so with any accuracy, but you should begin to see the difficulty one would have as a comparator manufacturer, trying to make a perfect ogive measuring tool for every bullet shape and every possible chamber reamer and one that allows for all possible tolerances in each of these items.

So what is a reloader to do? It’s simple. Understand that you are taking a relative measurement as compared to other samples of said same bullet and get on with life.

Edit: @whatsupdoc beat me to the post.

 

[AznTactical]

thanks for the input. Going forward I'm going to only use the Sinclair unit so when I measure my handloads I don't get that data mixed up with numbers from the Hornady comparator.

 

[lash]

That’s a good idea. With reloading, consistency and accuracy in practice makes all of the difference. Worry about the things that you can control and those that matter most. The rest will sort itself out.

 

[Carlos Danger]

Once I use a depth gauge I get a physical measurable representation of the bullet touching the lands. I then use the comparator to get a repeatable position on the bullet to make adjustments to the seating depth. You would do this same procedure even if you run the same weight bullet, but from different manufacturers.

 

[AznTactical]

What's frustrating is both Sinclair and Hornady advertise on their comparator's webpage that they're both coming off the bullet's O-give. When I'm getting a difference of .053" I'm calling b.s.

Hornady: "Our Bullet Comparator measures rounds from the ogive to provide consistent, precise measurements."

Sinclair: "measure and compare bullet ogive-to-base as well as loaded round ogive-to-cartridge-base measurements."

 

[Huskydriver]

What's frustrating is both Sinclair and Hornady advertise on their comparator's webpage that they're both coming off the bullet's O-give. When I'm getting a difference of .053" I'm calling b.s.

Hornady: "Our Bullet Comparator measures rounds from the ogive to provide consistent, precise measurements."

Sinclair: "measure and compare bullet ogive-to-base as well as loaded round ogive-to-cartridge-base measurements."

You are getting a base to ogive measurement..... How does Sinclair or Hornady know which of the thousands of bullet designs you are using? They don't so they machine the comparetor for usually the most popular bullet shape in a given caliber.

So your numbers are off the Sami spec drawing??? Who cares... Ogive measurement's like other reloading measurements are relative to YOUR chamber, comparetor etc etc. It's just a number you write it down and that's your bto measurement with your comparetor done deal.

 

[lash]

It’s sorta like buying a 2x4 at the local lumberyard. It’s a generic term used to express a concept. In both cases, the idea is a measurable dimension that can be verified, and in both cases, the matter of convenience for suppliers comes into play. The difference is that in the case of a 2x4, the vendors are selling you less and less product under the generic term.

 

[AznTactical]

You are getting a base to ogive measurement..... How does Sinclair or Hornady know which of the thousands of bullet designs you are using? They don't so they machine the comparetor for usually the most popular bullet shape in a given caliber.

You're missing my point. I had assumed a bullet insert comparator as marketed by Hornady and Sinclair touches the o-give point of any bullet type but for the same caliber. I did NOT know that they are falsifying this. Based on all of the answers to my question it only touches somewhere on the bullet's jacket and as long as I stick to 1 brand I can still be repeatable to load off the lands as long as I know COAL to give me BTO.

 

[2aBaC̶a̶]

You could color a bullet with a sharpie and find on the bullet exactly where your lands touch the ogive, then compare it to where both measuring devices contact it for reference.

I use the hornady and can see the aluminum bushing that measures the ogive getting worn with use.

Stainless would be better.

 

[Huskydriver]

You're missing my point. I had assumed a bullet insert comparator as marketed by Hornady and Sinclair touches the o-give point of any bullet type but for the same caliber. I did NOT know that they are falsifying this. Based on all of the answers to my question it only touches somewhere on the bullet's jacket and as long as I stick to 1 brand I can still be repeatable to load off the lands as long as I know COAL to give me BTO.

Lol how are they falsifying this? You got a bto measurement didn't you? Did they advertise an exact bto for a specific bullet on their website? No... They didn't it's a tool for getting an exact bto measurement for your bullet/caliber/barrel combo nothing more nothing less... You assume too much young Padawan ?. Every bullet styles ogive point will be different even across the same chambering

 

[2aBaC̶a̶]

@AznTactical does the Sinclair bushing fit in the Hornady body? I like the idea of stainless bushing.

 

[AznTactical]

@AznTactical does the Sinclair bushing fit in the Hornady body? I like the idea of stainless bushing.

I don't know. For the last 7 weeks I've been using Hornady bushing (it was available locally) in a Sinclair body. The Sinclair 6.5 creedmoor bushing was on backorder and I just got it Saturday.

 

[AznTactical]

You could color a bullet with a sharpie and find on the bullet exactly where your lands touch the ogive, then compare it to where both measuring devices contact it for reference.


Stainless would be better.

Yes I just did that and the witness marks are right over the Sinclair's bushing's location.

 

[2aBaC̶a̶]

Yes I just did that and the witness marks are right over the Sinclair's bushing's location.

Using the hornady can you see where the .05 difference lines up?

I don't know. For the last 7 weeks I've been using Hornady bushing (it was available locally) in a Sinclair body. The Sinclair 6.5 creedmoor bushing was on backorder and I just got it Saturday.

So it should work then? I would rather have the SS Sinclair bushing.

 

[Carlos Danger]

Past weekend I loaded 115 DTAC's and 105 Noslers. Set to same jump the 105's were near .004 longer OAL. Obvious the ogive of each is dramatically different.

 

[2aBaC̶a̶]

Looking at the Sinclair website description does the inside where the bullet ogive touches the bushing have a bevel? That could be where the .05 difference is coming from. The caliper zero isn't at the same point the bullet touches.

 

[AznTactical]

Using the hornady can you see where the .05 difference lines up?




So it should work then? I would rather have the SS Sinclair bushing.

Yes it should work.

 

[AznTactical]

Looking at the Sinclair website description does the inside where the bullet ogive touches the bushing have a bevel? That could be where the .05 difference is coming from. The caliper zero isn't at the same point the bullet touches.

Both Sinclair and Hornady have a very small beveled edge so that will throw the true BTO off.

 

[BIRDHUNTER]

Sinclair is cut with a 1’30” taper just like most chambers. Hornady does not. That’s why there is a difference in measurement. Sinclair will give you a better comparison if you are working off a reamer print. Is it perfect no, is it a more accurate measurement of the olive, yep.