Length to Ogive

[andydrose72]

This is just something I was thinking about since I want to try some different bullets in my gun. And I would just test it out if it was possible to find a 260 rem modified case. I'm hoping someone has tried it already and can tell me if its a bad idea. The rifleings in barrel are a constant diameter so the contact point on bullet should be a constant diameter. And your hornady comparator should be constant as well as the diameter were it is also contacting the bullet. So my question is if you have a length with the comparator on one bullet shouldn't it be the same when you go to another bullet? And I ask this knowing that the overall length will change.

 

[mdmp5]

It should be the same base to ogive distance regardless of the bullet used

 

[andydrose72]

Ok, thanks. I just wanted to make sure there wasn't something I was overlooking.

 

[F4D]

Every bullet has a different ojive dimension where it will contact the lands. A SMK verses a Berger verses a Scenar . I hope I am reading and understanding your post. Using one type of bullet set at a particular base to ojive and then using a different bullet can get you into trouble if you are seating to lands.

 

[mdmp5]

Every bullet has a different ojive dimension where it will contact the lands. A SMK verses a Berger verses a Scenar . I hope I am reading and understanding your post. Using one type of bullet set at a particular base to ojive and then using a different bullet can get you into trouble if you are seating to lands.

He is asking if the distance from ogive of land engagement to base will be the same regardless of bullet. It will. .300 will be at a different area on one bullet relative to another, but will seat accordingly to create the same length

 

[bruddah]

When I measure 5 different bullet types, I get 5 different readings to the lands so don't assume 2.809" to the lands on one bullet manufacturer (say Sierra) will be 2.809" on another brand such as Nosler/Berger/etc. They will not.

The ACTUAL distance to the lands may be the same, but the reading you get using your Hornady comparator will definitely NOT be the same due to the different shapes of the bullets.

I hope this is the question you were trying to get an answer to.

 

[andydrose72]

I guess that leaves me with another question then. I thought the comparator took a measurement were the bullet contacted the lands. What exactly are you measuring with the comparator then? Is it just to a more consistent spot on the bullet as meplats are far from uniform?

 

[bruddah]

I guess that leaves me with another question then. I thought the comparator took a measurement were the bullet contacted the lands. What exactly are you measuring with the comparator then? Is it just to a more consistent spot on the bullet as meplats are far from uniform?

The comparator does measure where the bullet contacts the lands. If one bullet has a slightly different profile, say sleeker or more blunt, it will skew the reading slightly. That's why you have to get a reading for each bullet type/manufacturer. We're not talking 1/2", just a few thousandths. but that few thousandths can bump your pressure dangerously high if you are going the wrong way and jamming into the lands.

 

[gstaylorg]

I have observed the same thing as bruddah...different bullets give different dimension to just touching when using the Hornady OAL gauge and calipers with the Hornady insert. One thing you'll notice if you compare the Hornady caliper insert with other brands like Sinclair is that the hole for a given caliber is actually smaller. Therefore it seats farther out on the ogive than do the inserts with holes closer in diameter to the actual caliber. There are both good points and bad that go along with using the Hornady inserts, but overall I generally prefer them. If you ever have to seat a bullet fairly deep in the case and/or trim your necks on the long side, the Sinclair insert seats very close to the case neck and can make it a little more challenging to get good readings.

To answer your question, when measuring your chamber with the Hornady OAL gauge (Stoney Point gauge), the nature of the tool means you have to rely on "feel" as the bullet approaches/touches the lands. Doing this consistently takes a bit of practice, but I don't find it very difficult. Because you are pushing the bullet to where it just touches the rifling, it is possible that there may be a difference in how you perceive the "touch" because of the different radii of curvature for the ogives of different bullets and how they behave when they encounter the initial angle of the lands in the throat.

However, it is much more likely that because the Hornady insert has a smaller hole and actually contacts the bullet much farther away from the bearing surface/ogive junction, you are simply contacting the different bullets at different points on the ogivewhen you measure, because their ogive radii are not the same. In other words, the diameter of the ogive at which different bullets contact the rifling is the same; obviously the bore/rifling diameter doesn't change just because you switched bullets. Because the Hornady comparator insert isn't actually contacting that point, but a point that matches the smaller diameter of the insert hole that is farther out on the bullet ogive, bullets with different ogive radii will change where the comparator insert seats on the bullet when you measure. The larger the difference in ogive radii between the bullets, the larger the distance between where the comparator insert will seat. Hence, the larger the discrepancy you will find when using this system to measure your chamber with different bullets.

The best way around this is to use a comparator insert that seats as close to the ogive/bearing surface as possible (ie. a larger hole). The Hornady insert is obviously not the best tool for this task because it seats farther out on the ogive. The closer the comparator insert seats to the bearing surface, the less discrepancy you will see between different bullets of the same caliber. Bottom line is that if you are using the Hornady OAL gauge in conjunction with Hornady comparator inserts, you will need to re-measure your chamber dimensions when switching to a different bullet. I don't find it to be that big of a deal, but it does mean a little more work when trying different bullets. Alternatively, just buy a comparator insert that seats closer to the bearing surface like the one below. They're not very expensive.

SINCLAIR INSERT STYLE BULLET COMPARATOR | Sinclair Intl


Edited to add: here are chamber measurements (CBTO, just touching the lands) I took from one of my rifles using the Hornady OAL gauge and calipers with the Hornady comparator insert (avg of 10, +/- SD, numbers not rounded off)

Berger 185 Juggernaut: 2.2130" +/- 0.0
Berger 168 Hybrid: 2.1927" +/- 0.0003"

Note that the difference between the two is approximately 20 thousands. As bruddah mentioned, that could make a big difference in pressure between loaded rounds depending on how far off the lands you typically start your charge weight testing. You're much better off (safer) either measuring the chamber separtely for each different bullet you use, or buying a comparator insert that seats closer to the bearing surface as mentioned above. Good luck.

 

[bruddah]

I have observed the same thing as bruddah...different bullets give different dimension to just touching when using the Hornady OAL gauge and calipers with the Hornady insert. One thing you'll notice if you compare the Hornady caliper insert with other brands like Sinclair is that the hole for a given caliber is actually smaller. Therefore it seats farther out on the ogive than do the inserts with holes closer in diameter to the actual caliber. There are both good points and bad that go along with using the Hornady inserts, but overall I generally prefer them. If you ever have to seat a bullet fairly deep in the case and/or trim your necks on the long side, the Sinclair insert seats very close to the case neck and can make it a little more challenging to get good readings.

To answer your question, when measuring your chamber with the Hornady OAL gauge (Stoney Point gauge), the nature of the tool means you have to rely on "feel" as the bullet approaches/touches the lands. Doing this consistently takes a bit of practice, but I don't find it very difficult. Because you are pushing the bullet to where it just touches the rifling, it is possible that there may be a difference in how you perceive the "touch" because of the different radii of curvature for the ogives of different bullets and how they behave when they encounter the initial angle of the lands in the throat.

However, it is much more likely that because the Hornady insert has a smaller hole and actually contacts the bullet much farther away from the bearing surface/ogive junction, you are simply contacting the different bullets at different points on the ogivewhen you measure, because their ogive radii are not the same. In other words, the diameter of the ogive at which different bullets contact the rifling is the same; obviously the bore/rifling diameter doesn't change just because you switched bullets. Because the Hornady comparator insert isn't actually contacting that point, but a point that matches the smaller diameter of the insert hole that is farther out on the bullet ogive, bullets with different ogive radii will change where the comparator insert seats on the bullet when you measure. The larger the difference in ogive radii between the bullets, the larger the distance between where the comparator insert will seat. Hence, the larger the discrepancy you will find when using this system to measure your chamber with different bullets.

The best way around this is to use a comparator insert that seats as close to the ogive/bearing surface as possible (ie. a larger hole). The Hornady insert is obviously not the best tool for this task because it seats farther out on the ogive. The closer the comparator insert seats to the bearing surface, the less discrepancy you will see between different bullets of the same caliber. Bottom line is that if you are using the Hornady OAL gauge in conjunction with Hornady comparator inserts, you will need to re-measure your chamber dimensions when switching to a different bullet. I don't find it to be that big of a deal, but it does mean a little more work when trying different bullets. Alternatively, just buy a comparator insert that seats closer to the bearing surface like the one below. They're not very expensive.

SINCLAIR INSERT STYLE BULLET COMPARATOR | Sinclair Intl


Edited to add: here are chamber measurements (CBTO, just touching the lands) I took from one of my rifles using the Hornady OAL gauge and calipers with the Hornady comparator insert (avg of 10, +/- SD, numbers not rounded off)

Berger 185 Juggernaut: 2.2130" +/- 0.0
Berger 168 Hybrid: 2.1927" +/- 0.0003"

Note that the difference between the two is approximately 20 thousands. As bruddah mentioned, that could make a big difference in pressure between loaded rounds depending on how far off the lands you typically start your charge weight testing. You're much better off (safer) either measuring the chamber separtely for each different bullet you use, or buying a comparator insert that seats closer to the bearing surface as mentioned above. Good luck.

Good writeup! I'm curious what kind of variation you see when using the Sinclair set up you just mentioned. If it makes THAT big of a difference, I'll just pick up a set of Sinclair inserts for ~ $15

 

[gstaylorg]

Picture is worth 1000 words:

As you can see for Berger 168 Hybrids, the bearing surface junction is pretty much buried in the Sinclair comparator insert, whereas it sits out quite a bit in the Hornady insert. The same will be true for any two different bullets with different ogive radii; how much farther out one bullet will sit is dependent on its ogive radius relative to the other bullet.

As I mentioned, I prefer the Hornady insert because it sits farther away from the case neck and I find it easier to get consistent measurements. As long as you use the same comparator insert every time and measure your chamber with each different bullet, it doesn't matter too much which one you use, it's all relative. I have a couple loads where the ogive/bearing surface junction is very close to the case neck and that makes it more difficult to use the Sinclair insert, which you can easily see the reason for in the picture. For that reason I gravitated toward the Hornady insert, but one does not really work any "better" than the other, you just need to be a little more careful with the Hornady insert and measure your chamber with every different bullet you use. I would do that anyhow, so it makes little difference to me.

I should also add that even very small differences in comparator inserts will cause the same phenomena. This is why CBTO measurements between two different people using different tools, even if they're the exact same brand, may not give the same cartridge dimensions and results.

 

[mdmp5]

The problem with the hornady or Sinclair comparator is that the opening of the insert is not the diameter of the land engagement. They are tapered down, so you will get a different reading with different bullets. However, if you use the redding instant indicator, you will see the same measurement between bullets because it uses a simple bushing to measure

 

[bruddah]

Picture is worth 1000 words:

As you can see for Berger 168 Hybrids, the bearing surface junction is pretty much buried in the Sinclair comparator insert, whereas it sits out quite a bit in the Hornady insert. The same will be true for any two different bullets with different ogive radii; how much farther out one bullet will sit is dependent on its ogive radius relative to the other bullet.

As I mentioned, I prefer the Hornady insert because it sits farther away from the case neck and I find it easier to get consistent measurements. As long as you use the same comparator insert every time and measure your chamber with each different bullet, it doesn't matter too much which one you use, it's all relative. I have a couple loads where the ogive/bearing surface junction is very close to the case neck and that makes it more difficult to use the Sinclair insert, which you can easily see the reason for in the picture. For that reason I gravitated toward the Hornady insert, but one does not really work any "better" than the other, you just need to be a little more careful with the Hornady insert and measure your chamber with every different bullet you use. I would do that anyhow, so it makes little difference to me.

Good to know.
Hmm... Picture not coming through for me..

EDIT:
Picture is now working. Looks like a dramatic difference! Thanks for sharing!

 

[bruddah]

The problem with the hornady or Sinclair comparator is that the opening of the insert is not the diameter of the land engagement. They are tapered down, so you will get a different reading with different bullets. However, if you use the redding instant indicator, you will see the same measurement between bullets because it uses a simple bushing to measure

Thanks for the info. I'll have to look into that.

 

[bruddah]

Picture is worth 1000 words:

As you can see for Berger 168 Hybrids, the bearing surface junction is pretty much buried in the Sinclair comparator insert, whereas it sits out quite a bit in the Hornady insert. The same will be true for any two different bullets with different ogive radii; how much farther out one bullet will sit is dependent on its ogive radius relative to the other bullet.

As I mentioned, I prefer the Hornady insert because it sits farther away from the case neck and I find it easier to get consistent measurements. As long as you use the same comparator insert every time and measure your chamber with each different bullet, it doesn't matter too much which one you use, it's all relative. I have a couple loads where the ogive/bearing surface junction is very close to the case neck and that makes it more difficult to use the Sinclair insert, which you can easily see the reason for in the picture. For that reason I gravitated toward the Hornady insert, but one does not really work any "better" than the other, you just need to be a little more careful with the Hornady insert and measure your chamber with every different bullet you use. I would do that anyhow, so it makes little difference to me.

I should also add that even very small differences in comparator inserts will cause the same phenomena. This is why CBTO measurements between two different people using different tools, even if they're the exact same brand, may not give the same cartridge dimensions and results.

One more question for you. It looks like the inserts are interchangeable with the holder (IE Sinclair inserts will fit into a Hornady gage body and vice versa?) If so that'll save me about $16 if I just order the inserts.
Thanks!

 

[gstaylorg]

bruddah, the inserts are interchangeable, at least with the Sinclair comparator body.

mijp5 - I took a look at the Redding tool, thanks for the info. It's a little pricey, but I can see where it would be a useful addition to the reloading tool box. I understand what it does, but it's not clear to me when you would actually use it. Specifically, how/where do you fit that tool into your reloading routine?

 

[mdmp5]

bruddah, the inserts are interchangeable, at least with the Sinclair comparator body.

mijp5 - I took a look at the Redding tool, thanks for the info. It's a little pricey, but I can see where it would be a useful addition to the reloading tool box. I understand what it does, but it's not clear to me when you would actually use it. Specifically, how/where do you fit that tool into your reloading routine?

It really is meant to be used on a turret press, like the t7. You seat a bullet, measure on the indicator, seat again with adjustment, and measure again.

 

[zulu1delta]

So I need to measure every bullet in my chamber with the Stoney Point tool? I measured a 168 match bullet and when seated in a dummy round, say got a .048 on the RCBS precision mic. I have been seating other brand match bullets to read .048 on the precision mic. Does this give me the same ogive engagement point or have I been screwing up thinking the engagement point was the same?. I thought if you matched the ogive reading (.048) that it was the same for any bullet as you are adjusting to the same point. Am I wrong?

 

[gstaylorg]

Thanks, I get that part. What I was really asking is how can that tool be used to determine distance to the lands in a chamber when using different bullets, which was the the focus of the discussion. I understand its use during seating, but was wondering if you had come up with a way to use it to actually measure the chamber, thus getting around the use of something like the Stoney Point gauge and comparator inserts. I still don't see how it could easily be used for that, unless perhaps you were seating dummy rounds out until the lands started to engrave, then used the Redding tool to measure the dummy rounds. Otherwise, it seems as if you'd still need to use a Stoney Point gauge and comparator insert at least once to get the initial seating depth figured out. Presumably, once you have the seating depth your after with one bullet, the Redding tool would allow you to get the same seating depth with a different bullet, without re-measuring the chamber or worrying about differences between comparator inserts, correct?

 

[gstaylorg]

zulu - look at the picture I posted, using the Hornady comparator insert on the left as an example. It seats/measures way out on the ogive from the bearing surface junction because it has a hole much smaller than the diameter of a .308 bullet at it widest point on the bearing surface. It will seat to the same diameter every time, BUT that diameter will not be at the same place in relation to the bearing surface junction if you measure a bullet with a different ogive radius. The point at which the comparator insert seats may be closer or farther away from the bearing surface junction, but it will not be the same distance as the other bullet. If the bullet shape is very, very close, you may not notice a big difference.

The mic on your seater die only controls how far in the seater stem is positioned in the die. The number on the mic dial really has no direct relation to the bullet ogive or where the bullet ogive will end up in a loaded round, because the seater stem pushes from out at the tip of the bullet. So it is analogous in a way to the different diameter holes in different comparator inserts, because the stem contacts and pushes in on the end of the bullet, not the ogive/bearing surface. For that reason, a typical seating die will NOT put the ogive/bearing surface in the same place for two different bullets because their noses are not the same length. By starting your seating long, you can easily dial the mic in until you determine the setting for THAT SPECIFIC bullet. That setting will even vary somewhat with a single type/lot of bullets, particularly if the OAL of your specific lot of bullets has significant length variation. It will definitely be off if you use a different bullet that has a different nose length.

You really want to be measuring the distance to your lands using either A) a method that is completely independent of bullet type, or B) measure for each bullet type you try if using the Stoney Point gauge and comparator inserts. To be honest, I'm not sure how to accurately do A). It seems to me that at some point in the loading process, you will still always have to make a measurement based off the bullet ogive that can be related in a reproducible way to the distance to lands measurement. It wouldn't surprise me if such a method or tool exists, but the Stoney Point gauge and comparator insert system has been working very well for me (even though I have to measure for every bullet), so I've never really looked to see if there is a better way.

 

[zulu1delta]

So I need to find the ogive engagement point in my chamber for each bullet I use with the Stoney point tool and the RCBS mic? On the RCBS mic one bullet might be 048, another 052, another 065 depending on the individual bullet ogive where they "zero" on the lands/grooves?

 

[gstaylorg]

That is what I do and it seems to work reasonably well. You can make an educated guess based on the mic setting for one bullet where it needs to be for another; it may or may not put you close. As long as you seat long to start, you can always adjust in until you reach the desired CBTO. I typically check first by seating a couple dummy rounds in junk brass I have laying around to get close, but not past the desired seating depth. I pull those bullets and load them again for use as fouling shots.

The seating depth can be fine tuned when you're actually loading rounds, if necessary. Record the mic setting for future use. You can also mark the mic dial with different color sharpies for different bullets or seating depths if you want. I haven't found that necessary, but some like to do it. If I accidentally push one in too far, I'll set it aside as a fouler. For me, the increments on the mic have been pretty close adjustment-wise once I have a loaded round that is near the correct seating depth that I can actually measure with the calipers. Depending on the length variation in any given lot of bullets you're loading, you also may have to tweak the mic to get each round seated right where you want it. I have been loading various flavors of Berger .308 and .224 bullets and have not found it necessary to do that. But that may not be true for all lots or manufacturers.