Weird. Three bullets, two different lengths to the lands.

[#40Fan]

Using the Hornady OAL gauge I was checking the length to the lands on one of my rifles. I was using a 107 grain SMK. Repeatable numbers at 2.280", CBTO. For some reason I decided to check with a 110 grain SMK. Repeatable 2.268", CBTO. Thought, that is weird. Tried measuring two different ways. Pushing the bullet into the lands with the gauge and setting the bullet long and allowing it to push the center rod of the OAL gauge back. Same two different measurement. S's & G's, I put a 70 grain Blitzking in the tool, repeatable 2.268", CBTO. Tried different 107 grainers as well.

Edited to add the C to the BTO.

 

[dsculley]

No mystery. You are not actually measuring the length of the base to the ogive where it meets the bore. You are measuring the length to the datum set by your gauge when the bullet is seated with the ogive at the lands. Your tool does not have the same diameter as the bore in your barrel. Since the three bullets are shaped differently you are getting different measurements.

 

[dnellans]

What seems weird about this? Different bullets have different base to ogive (where bullet touches the lands) distances. You should -expect- different bullets to have different seating depth to be touching the lands.

Maybe I'm misunderstanding the question.

 

[#40Fan]

No, you're not misunderstanding. I was under the impression the ogive of the bullet would touch the lands in the same spot, no matter the bullet. If the tool I am using isn't measuring to the ogive of the bullet, then that is where I made the mistake.

 

[rammac]

The bushing for the Hornady tool has a hole that matches (theoretically) the diameter of the bullet at the ogive's datum line. The location of that diameter, along the distance of the bullet's length, is different for every weight/style of bullet. The headspace tool is intended to give you a relative comparison, from one bullet to another, of that distance along the bullet's length. To use the headspace tool properly you need to find the seating depth first and then measure the distance from the base of the cartridge to the bullet's ogive and then record that dimensional value for future use. The OAL tool is another comparative tool that is supposed to be used with the specific bullet you intend to use and it finds the seating depth required to touch the lands. You are supposed to use the tool to find the lands with your bullet of choice. After your bullet is seated to the lands you measure the dimension to the ogive with the headspace tool, then you record that headspace dimension for that bullet. All of these dimensions are relative comparisons and not true measurements.

 

[SteveOak]

There is also the leade to consider.

Leade
There is a short section of the chamber in front of the throat where the rifling begins. Rather than have an abrupt step from freebore to fully rifled, there is a conical transition. This is known as the leade. You'll see a few standard angles for this - often it's 1.5 degrees.

Because the leade is angled and you are looking at bullets with different ogives, it would stand to reason that the bullets would contact the leade at different distances from the bolt face.

http://pictures.bisonballistics.com/chamber-neck-diagram@2x.png

The reason that Eley will usually perform best in an Anschutz rifle is that Anschutz uses reamers with a leade angle that is most suitable to the shape of the Eley bullet.

I have often wondered if there may be a similar phenomenon at play in centerfire rifles.

 

[hogpatrol]

As previously posted, Not to be unexpected. Different ogive radius touches at a different point on the lead angle. Bullets of two different weights, same diameter, of the same ogive radius should touch at the same point.

Examples: 95 SMK Ogive radius=2.803
107 SMK Ogive radius=2.763



https://sierrabulletsblog.com/2016/12/28/what-is-caliber-of-ogive/

Edited: replaced caliber with radius.

 

[mtang45]

No mystery. You are not actually measuring the length of the base to the ogive where it meets the bore. You are measuring the length to the datum set by your gauge when the bullet is seated with the ogive at the lands. Your tool does not have the same diameter as the bore in your barrel. Since the three bullets are shaped differently you are getting different measurements.

Yep, the hole in tool is not the exact same diameter as the ogive on the bullet. if you could measure "exactly" on the ogive the readings would be the same for all bullets for that chamber. Since its not the same diameter as the ogive, that relative diameter can be different distances from the actual ogive depending on the bullet shape.

 

[spife7980]

This isnt exactly what the image is pointing out but its still illustrative.
You can see that the different orange lines are different bullet profiles and that the blue and green are different lands. Different combos of one or the other or both can lead to different results.

The bullets parabolic curve and the lands linear angle arent all the same.

 

[SteveOak]

Yep, the hole in tool is not the exact same diameter as the ogive on the bullet. if you could measure "exactly" on the ogive the readings would be the same for all bullets for that chamber. Since its not the same diameter as the ogive, that relative diameter can be different distances from the actual ogive depending on the bullet shape.

Maybe you have your terms mixed up or I don't understand what you are saying.

"Ogive" is the curved part of the bullet between the point and where the bullet is full bore diameter.

Any insert with a hole that is larger than the point and smaller than the bore diameter will cause the bullet to contact somewhere.

Two bullets with different ogives will penetrate the insert to a different depth.


On a slightly different topic. It would be advantageous to have an insert that was cut with the same reamer as your chamber. Then it would contact the bullet at the same place as the chamber would.

 

[dsculley]

For you to better understand this, use your test case and bullet. Color the bullet with a marker so you can see where the lands touch the bullet. Remove the case and slide your comparator over the bullet. You will see that where it meets the bullet does no coincide with where the lands met the bullet.

 

[mtang45]

Maybe you have your terms mixed up or I don't understand what you are saying.

"Ogive" is the curved part of the bullet between the point and where the bullet is full bore diameter.

Any insert with a hole that is larger than the point and smaller than the bore diameter will cause the bullet to contact somewhere.

Two bullets with different ogives will penetrate the insert to a different depth.


On a slightly different topic. It would be advantageous to have an insert that was cut with the same reamer as your chamber. Then it would contact the bullet at the same place as the chamber would.

Steve, let me clarify because after reading all the responses, I'm thinking the OP is still scratching his head.

First the ogive is the arc of the bullet from the shank to the tip (meplat). What the OP is measuring is the distance from the base of his cartridge to a point on the ogive when the ogive of the bullet is touching the lands.

The reason the OP is getting different measurements for two different bullets is because the Hornady tool is a static hole size that probably does not represent the actual diameter of the bullet at the point where it makes contact with the lands. However, it does allow a user to make relational comparisons on that measurement as long as you are measuring the same caliber, weight, model and manufactures bullet. When you change to a different bullet of the same caliber, all bets are off and you need to measure again to establish the new dimensional relationship for that bullet.

I'm sure that's clear as mud. Sorry but I had the same questions in my head several years ago. It wasn't until I made the connection that I was NOT measuring my chamber but measuring a bullet for its relationship to my chamber and that changes with different bullet shapes, that it finally all came together for me.

 

[JohnKielly]

It would be advantageous to have an insert that was cut with the same reamer as your chamber. Then it would contact the bullet at the same place as the chamber would.

... until your throat started to wear...

 

[#40Fan]

It wasn't until I made the connection that I was NOT measuring my chamber but measuring a bullet for its relationship to my chamber and that changes with different bullet shapes, that it finally all came together for me.

That is exactly what confused me. I thought the tool measured the same spot on the bullet, which it does, which coincided with where it touches the rifling....obviously doesn't.

 

[SteveOak]

... until your throat started to wear...

Yeah, there is that. LOL

 

[hogpatrol]

That is exactly what confused me. I thought the tool measured the same spot on the bullet, which it does, which coincided with where it touches the rifling....obviously doesn't.

The Hornady tool gives a reference dimension only. The tool does not replicate the chamber.

 

[grovey]

The Hornady tool gives a reference dimension only. The tool does not replicate the chamber.

+1

 

[CaptainMal]

What is frustrating is to buy a lot of bullets. Use your measuring tool and see different measures on the SAME BULLET LOT for different bullets. Poor quality control leads to that issue. I have Berger Hybrids and Sierra SMK's that measure out so differently it makes you think there are different brands and styles of bullets mixed in to the same box.

That measurement difference is why many shooters "sort" bullets by both weight and ogive datum measure, using ones near the same to shoot their groups.

 

[JFrank]

What is frustrating is to buy a lot of bullets. Use your measuring tool and see different measures on the SAME BULLET LOT for different bullets. Poor quality control leads to that issue. I have Berger Hybrids and Sierra SMK's that measure out so differently it makes you think there are different brands and styles of bullets mixed in to the same box.

That measurement difference is why many shooters "sort" bullets by both weight and ogive datum measure, using ones near the same to shoot their groups.

Don't say That!
I just ordered 500 107 smk
J

 

[Dusty Stevens]

What is frustrating is to buy a lot of bullets. Use your measuring tool and see different measures on the SAME BULLET LOT for different bullets. Poor quality control leads to that issue. I have Berger Hybrids and Sierra SMK's that measure out so differently it makes you think there are different brands and styles of bullets mixed in to the same box.

That measurement difference is why many shooters "sort" bullets by both weight and ogive datum measure, using ones near the same to shoot their groups.

Which is why lot numbers mean nothing to a mass produced bullet except they were packaged together