Interesting Find, Bullet Base to Ogive...

kilotanker22 · May 19, 2021, 10:21 PM

Recently I switched bullets in my 6.5 Creedmoor from the 140 grain Nosler Custom Competition bullet, to the 145 grain Barnes Match Burner. The obvious reason for me was the high G7 BC value. I bought a box of 100 bullets at first and they shot pretty well and were reasonably consistent, so I bought 1000 more.

Fast forward a few hundred bullets and all of a sudden my .25-.3 moa rifle became a 1 moa rifle. I have never shot it very warm and I am only a few hundred rounds down the tube anyway so I am not worried about the barrel.

Velocity had not changed any discernable amount and velocity spread is still the same so I ruled out my powder and primer. My case prep is also not the issue, (I painstakingly make sure that every single case is identically prepped and sized. Any cases with any variation from nominal after sizing is set aside and used for warm up/practice.

Next I looked to my bullet seating. I had just ten rounds still loaded so I decided to measure the cartridge base to ogive and the cartridge base to shoulder datum, looking for something out of whack. I found the cartridge base to datum measurement on all ten cases to have less than .0005 variance across the lot of ten. I then measured cartridge base to ogive and found a runout of .008"... Not OAL, this was CBTO. I pulled those ten bullets and measured bullet base to ogive and found about the same variance between them.

Due to the ogive location variance of the bullets, my distance to the lands is varying by as much as .008". This brings me to the conclusion that the changes in barrel time and harmonics is what increased my average group size. I do understand that 1moa is still an ok shooter, but this is a quarter minute rifle and load, not 1moa.

To verify that this was not a mistake I made by potentially mixing lots, I checked all of my boxes and this box of 500 is the only one open, so all of the bullets came from that box. Then I took a sample of 50 and measured an overall variance of about .008" across the sample of 50. I did not bother to calculate the standard deviation, but observed about 20% of the bullets at the lower end and about 20% at the higher end of the measurements. The rest were pretty consistent with only .001-.002" variance across approximately 60% of the sample.

I opened a second 500 count box and measured a sample of 50. I found no more than .002" variance across the entire sample for the bullet base to ogive measurement. I also decided to compare these to the 250 count box of Nosler Custom Competition bullets that I have left. I took a sample of 50 bullets from the Nosler box and found less than .001" extreme spread across the entire sample. Now I need to decide to keep using the Barnes, of which I have around 1000 bullets, or to switch back to the Noslers, or find another bullet.

I am thinking maybe I just got a less than perfect box of bullets. I do wonder if Barnes might replace them. I am not upset really, just figured I would share an experience that had me baffled for a few days.

Before anyone says it, I have checked the rifle and optic thoroughly. I am nearly certain that the bullet is my problem. I guess the next step is to test the other lot of bullets to see if the problem persists.

**44 AMP** · May 19, 2021, 10:47 PM

I suppose you should talk to the people who made the bullets and see if they have a spec for the distance you are measuring and if they do, see if they suspect bullets are within it, or not.

However, there might be a communication issue, because "ogive" is not a point.

All my loading manual glossaries and other tech references are consistent in their definition of ogive, and it is not a point, it is the entire curved or sloped portion of the bullet, from the point it reduces from full caliber diameter forward. Even the non technical dictionaries define ogive as a pointed arch.

As I understand the definition, you are not measuring to the ogive, you are measuring from the base to a point on the ogive of the bullet.

That point is being determined entirely by you, so I think communication issues over exactly what you mean and what point on the ogive you are using are very likely to happen.

If, for example, you are measuring from the base to the point on the ogive where the bullet contacts the rifling in your gun, no one else is going to know where that is. And that point on the bullet where it contacts the rifling can be and normally is slightly different in each different barrel, so someone else's numbers with their barrel are worthless to you just as yours are worthless to them.

Or so it seems to me...

kilotanker22 · May 19, 2021, 11:23 PM

I guess my point is that with the same diameter on the ogive of the varying in distance from the base of the bullet to that point on the ogive, is giving me random seating depth measurements. Essentially changing the distance that each bullet jumps to the lands. I will try to call Barnes tomorrow and see if they have a standard for that. Even so, when measured with the same comparator, different lots, and even different brands with different ogive shapes, I should get a measurement more consistent than what I got. As was shown by the same bullet from another lot and another brand bullet.

Colorado Redneck · May 19, 2021, 11:40 PM

Kilo
How many rounds down the tube on your 6.5? And have you measured bolt face to lands and compared to your starting measurement? I had a CZ in 222 Remington the lands were .4 inches farther from bolt face by the time I sold it. Had to chase the lands to keep accuracy. Just an idea, and I am not pretending to be a guru.

Shadow9mm · May 20, 2021, 12:29 AM

So one question. How did you set your seating depth? Is it possible it just needs to be tuned a bit with this new bullet to get into a good spot in the barrels harmonic? After I test for powder load consistent I generally work back from the lands in 0.003 increments to find the best harmonic point in the barrel.

hounddawg · May 20, 2021, 06:00 AM

Just pulling some #s outta my keister here but sort the bullets so you have all the ones measuring 1.000 1.001 1.002 into one box 1.003 1.004 1.005 in another 1.006 1.007 1.008 in a third box. Then you have 1000 bullets measuring plus or minus .001 of each other. Start with the shortest box set the seating depth for 1.001 and when you shoot all those, adjust seating depth out .003 for the next box etc etc

or sell them on gunbroker and get your money back

jetinteriorguy · May 20, 2021, 06:23 AM

Another thought, you may have settled on a seating depth with a very small window for accuracy, it may be possible by going deeper you will discover a depth with a larger window to allow for these bullet variances.

cdoc42 · May 20, 2021, 07:19 AM

Kilotanker, more than a few years ago I tried Barnes in my .270 and came across a recommendation from Barnes that the bullets should be seated no closer than 0.05" from the lands. No details. But I suspected the manufacturing process produced variations in the bullet base to ogive that lead to that recommendation.

Bart B. · May 20, 2021, 08:41 AM

Some bullet companys mix bullets from different forming die setups and are not shaped identical. Ask them if they do.

hounddawg · May 20, 2021, 09:32 AM

The 6.5 140gn Barnes MB's seated .025 off lands in my .260 and the 6mm 105 gn seated to magazine length in my 6 ARC both give me good results. At least as good as the Bergers of the same weight/caliber. On another forum there is a thread and it seems no one has had much luck with those 145's. Someone said they copper up the barrel bad also but I have never had any issues with the ones I have shot

kilotanker22 · May 20, 2021, 12:41 PM

Quote:

Originally Posted by Shadow9mm

So one question. How did you set your seating depth? Is it possible it just needs to be tuned a bit with this new bullet to get into a good spot in the barrels harmonic? After I test for powder load consistent I generally work back from the lands in 0.003 increments to find the best harmonic point in the barrel.

This is a variation in bullets within the same box of 500. From a sample of 50 pieces, none of my other boxes experience the same variation. I tested this across several boxes of the same bullets, and another brand. It is not my die.

kilotanker22 · May 20, 2021, 12:48 PM

Quote:

Originally Posted by hounddawg

Just pulling some #s outta my keister here but sort the bullets so you have all the ones measuring 1.000 1.001 1.002 into one box 1.003 1.004 1.005 in another 1.006 1.007 1.008 in a third box. Then you have 1000 bullets measuring plus or minus .001 of each other. Start with the shortest box set the seating depth for 1.001 and when you shoot all those, adjust seating depth out .003 for the next box etc etc

or sell them on gunbroker and get your money back

The .008" variance was within just one box of bullets. The other boxes all have less than .002" variation. Also, nominal measurement with my comparator insert from bullet base to ogive is .740" all of my boxes have the same nominal value with most of the variance being from this one box of 500. I do not intend to measure each of the 100 bullets I have left and sort them based on bullet base to ogive. I may just sell them....

When I first started using this bullet was when I installed the new barrel on this rifle a few months ago. CBTO at the lands has not changed. For this comparison I used the same bullet I used to first measure this when the barrel was new and the same modified case. It just so happens that my Hornady modified case has the same cartridge base to shoulder datum as my sized and prepped brass so I don't have to worry about variation in the datum measurement impacting seating depth.

kilotanker22 · May 20, 2021, 12:50 PM

Quote:

Originally Posted by Shadow9mm

So one question. How did you set your seating depth? Is it possible it just needs to be tuned a bit with this new bullet to get into a good spot in the barrels harmonic? After I test for powder load consistent I generally work back from the lands in 0.003 increments to find the best harmonic point in the barrel.

I have used this method with success so far. Now I am using a tuner. I kept the seating depth the same as before and using the tuner to improve accuracy. However, if each of my bullets are jumping a different distance to the lands, the tuner can't really do the job it was intended to do.

kilotanker22 · May 20, 2021, 01:02 PM

Quote:

Originally Posted by Bart B.

Some bullet companys mix bullets from different forming die setups and are not shaped identical. Ask them if they do.

This is my leading theory at this point. I will try to find the time to call Barnes today and ask them.

kilotanker22 · May 20, 2021, 01:15 PM

I just got off of the phone with Barnes. They said that they do not mix bullets from different machines or lots. All of the bullets in a specific lot come from the same run on the same machine. That is at least pertaining to the bullet in question.

hounddawg · May 20, 2021, 01:31 PM

just checked a bunch of Barnes 175 30 cal MB's and only had .001 difference between the 25 that I checked, but thanks for the heads up. Now I will check a sample from every box before loading them

Brian Pfleuger · May 20, 2021, 01:50 PM

The most obvious solution is to modify your seating plug (or purchase a die) so that it touches the bullet at the ogive.

I generally use cheap, standard Lee seating dies and the seating plug always touches near the tip. I just drill them out to a size that's closer to ogive.

Bart B. · May 20, 2021, 04:27 PM

Let's hope Barnes changes lots if they adjust the bullet's pointing die that shapes the bullet ogive.

Meanwhile, note the place on the bullet's ogive that touches the rifling is about .002" smaller than the bullet's diameter.

higgite · May 20, 2021, 08:21 PM

Quote:

Originally Posted by kilotanker22

I just got off of the phone with Barnes. They said that they do not mix bullets from different machines or lots. All of the bullets in a specific lot come from the same run on the same machine. That is at least pertaining to the bullet in question.

Did they have any comment on the larger than normal BTO variations that you saw in that one box of bullets?

kilotanker22 · May 20, 2021, 10:21 PM

They wanted to know what lot they were from and the guy said he would call me back after he got the lot number from me. I emailed them a photo of the label when I got home from work today.

They did not have a comment on the variance I saw, but the gentleman seemed to be surprised by my results. He said he will get to the bottom of it and contact me.

kilotanker22 · May 20, 2021, 10:23 PM

That is a good point Bart. One that I knew was true, but also a point that does not get thought about often.

Mike / Tx · May 21, 2021, 08:59 AM

While I don't use as many as I used to, when I was running Barnes they were always on top of their game.

I've spoken to their techs quit a fee times thru the years and they have always gotten back to me in a timely manner, if they didn't have the answer immediately.

Nowadays I just don't have a need for as many as I used to, so generally use something a bit less expensive .

**Unclenick** · May 21, 2021, 11:24 AM

Kilotanker22,

Several things:

First, I suspect Brian may have given you the answer. If I understand correctly, you switched to a longer bullet shape. If the nose of the bullet is hitting the seating die stem way up inside before the opening in the seating stem's recess makes contact with the ogive, you will get seating depth variation equal to overall bullet length variation, and with hollow point match bullets, that can easily be 0.008" or so (I've measured up to 0.015" length variation on 30 cal Sierra MatchKings). Pull the seating stem out and look to see that a bullet dropped into it can't wiggle side-to-side because the tip bottomed out before the mouth of the stem opening makes contact.

Second, note that cartridges are pushed forward into any available headspace during firing. The Courtneys have measured ignition delays from the moment of firing pin impact to be between about a millisecond and a half to three milliseconds or so, IIRC. A forward cartridge velocity of just 1.7 inches per second will cover 0.002" of excess headspace in the time it takes for the powder pressure to start getting serious, and most rifle firing pins shove a case forward faster than that, especially when the primer backing out adds its thrust into the story. My point is, a rimless cartridge will have its shoulder pushed against the shoulder of the chamber as the case starts to expand and stick the body to the chamber. That means what is setting the bullet jump is not the CBTO, but the case shoulder-to-ogive distance. So if you want to check your bullet jump precisely, that's the number you want to measure. Only if your case head-to-shoulder measurements are exactly identical, will CBTO give you an identically accurate measurement to the shoulder-to-ogive measurement.

Third, as Bart pointed out, the actual diameter at which the bullet contacts the throat is just ahead of the shoulder where the ogive begins to depart from the cylindrical bearing surface portion of the bullet profile. If you are using a Hornady caliper comparator rather than the RCBS Precision Mic, Sinclair makes nice stainless comparator inserts that are shaped to mimic a chamber throat and that contact the ogive way down there, unlike the aluminum Hornady inserts. These inserts fit the Hornady caliper adapters, so it is only the insert you want to upgrade if you don't have one already. Part #090264.

Once you have that, you can use the Hornady case comparator insert to first check and record the head-to-shoulder measurement for each case. Then put the Sinclair insert in and get the head-to-ogive measurement with it. Subtract the first number from the second for each round. That will give you the actual bullet jump variation.

If your seating stem does leave the usual ring mark from properly contacting the ogive, put a comparator insert (brand doesn't matter here) into your caliper adapter that meets the bullet where the seating stem does. Measure a bunch of your bullet base-to-ogive with that insert and again with the Sinclair insert and see how much the difference varies. That will give you the contribution ogive shape inconsistency contributes to your jump.

Finally, note that if your seating stem is contacting the bullet ogive properly, any extra distance to the bullet base from the ogive will simply be pushed that much deeper into the case neck during seating. It should not affect bullet jump the way seating from tip contact with the bottom of the seating stem will, as long as the ogive contour coming off the bearing surface is consistent. That last test I mentioned will determine that.

kilotanker22 · May 21, 2021, 11:44 AM

Thanks Unclenick, I will double heck for these things this weekend when I am off work.

Rimfire5 · May 21, 2021, 05:52 PM

kilotanker22,

I think Unclenick has given you the answer.
That said, I measure cartridge base to ogive on every round I load and I have never seen that amount of variation on loaded rounds and I have loaded over 53,000 rounds with all kinds of bullets.

Also, having purposely varied the jump on different loads to optimize the jump for a particular bullet, my results show that a change of 0.008 in effective jump is not catastrophic enough to change the average group size by 0.7 inches at 100 yards.
It might change the average group size by 0.050 to 0.1 but never 7 times that.

Even massive velocity changes don't make that much difference in group sizes from a barrel that shoots 0.25 to 0.3 inch groups.
I suspect that there might be a factor other than jump at play to create that amount of growth in average group size.

May 19, 2021, 10:21 PM	#1
kilotanker22 Senior Member Join Date: October 14, 2012 Location: North Central, PA Posts: 2,127	Interesting Find, Bullet Base to Ogive... Recently I switched bullets in my 6.5 Creedmoor from the 140 grain Nosler Custom Competition bullet, to the 145 grain Barnes Match Burner. The obvious reason for me was the high G7 BC value. I bought a box of 100 bullets at first and they shot pretty well and were reasonably consistent, so I bought 1000 more. Fast forward a few hundred bullets and all of a sudden my .25-.3 moa rifle became a 1 moa rifle. I have never shot it very warm and I am only a few hundred rounds down the tube anyway so I am not worried about the barrel. Velocity had not changed any discernable amount and velocity spread is still the same so I ruled out my powder and primer. My case prep is also not the issue, (I painstakingly make sure that every single case is identically prepped and sized. Any cases with any variation from nominal after sizing is set aside and used for warm up/practice. Next I looked to my bullet seating. I had just ten rounds still loaded so I decided to measure the cartridge base to ogive and the cartridge base to shoulder datum, looking for something out of whack. I found the cartridge base to datum measurement on all ten cases to have less than .0005 variance across the lot of ten. I then measured cartridge base to ogive and found a runout of .008"... Not OAL, this was CBTO. I pulled those ten bullets and measured bullet base to ogive and found about the same variance between them. Due to the ogive location variance of the bullets, my distance to the lands is varying by as much as .008". This brings me to the conclusion that the changes in barrel time and harmonics is what increased my average group size. I do understand that 1moa is still an ok shooter, but this is a quarter minute rifle and load, not 1moa. To verify that this was not a mistake I made by potentially mixing lots, I checked all of my boxes and this box of 500 is the only one open, so all of the bullets came from that box. Then I took a sample of 50 and measured an overall variance of about .008" across the sample of 50. I did not bother to calculate the standard deviation, but observed about 20% of the bullets at the lower end and about 20% at the higher end of the measurements. The rest were pretty consistent with only .001-.002" variance across approximately 60% of the sample. I opened a second 500 count box and measured a sample of 50. I found no more than .002" variance across the entire sample for the bullet base to ogive measurement. I also decided to compare these to the 250 count box of Nosler Custom Competition bullets that I have left. I took a sample of 50 bullets from the Nosler box and found less than .001" extreme spread across the entire sample. Now I need to decide to keep using the Barnes, of which I have around 1000 bullets, or to switch back to the Noslers, or find another bullet. I am thinking maybe I just got a less than perfect box of bullets. I do wonder if Barnes might replace them. I am not upset really, just figured I would share an experience that had me baffled for a few days. Before anyone says it, I have checked the rifle and optic thoroughly. I am nearly certain that the bullet is my problem. I guess the next step is to test the other lot of bullets to see if the problem persists. __________________ “We do not seek peace in order to be at war, but we go to war that we may have peace. Be peaceful, therefore, in warring, so that you may vanquish those whom you war against, and bring them to the prosperity of peace. – St. Augustine

May 19, 2021, 10:47 PM	#2
44 AMP Staff Join Date: March 11, 2006 Location: Upper US Posts: 30,501	I suppose you should talk to the people who made the bullets and see if they have a spec for the distance you are measuring and if they do, see if they suspect bullets are within it, or not. However, there might be a communication issue, because "ogive" is not a point. All my loading manual glossaries and other tech references are consistent in their definition of ogive, and it is not a point, it is the entire curved or sloped portion of the bullet, from the point it reduces from full caliber diameter forward. Even the non technical dictionaries define ogive as a pointed arch. As I understand the definition, you are not measuring to the ogive, you are measuring from the base to a point on the ogive of the bullet. That point is being determined entirely by you, so I think communication issues over exactly what you mean and what point on the ogive you are using are very likely to happen. If, for example, you are measuring from the base to the point on the ogive where the bullet contacts the rifling in your gun, no one else is going to know where that is. And that point on the bullet where it contacts the rifling can be and normally is slightly different in each different barrel, so someone else's numbers with their barrel are worthless to you just as yours are worthless to them. Or so it seems to me... __________________ All else being equal (and it almost never is) bigger bullets tend to work better.

May 19, 2021, 11:23 PM	#3
kilotanker22 Senior Member Join Date: October 14, 2012 Location: North Central, PA Posts: 2,127	I guess my point is that with the same diameter on the ogive of the varying in distance from the base of the bullet to that point on the ogive, is giving me random seating depth measurements. Essentially changing the distance that each bullet jumps to the lands. I will try to call Barnes tomorrow and see if they have a standard for that. Even so, when measured with the same comparator, different lots, and even different brands with different ogive shapes, I should get a measurement more consistent than what I got. As was shown by the same bullet from another lot and another brand bullet. __________________ “We do not seek peace in order to be at war, but we go to war that we may have peace. Be peaceful, therefore, in warring, so that you may vanquish those whom you war against, and bring them to the prosperity of peace. – St. Augustine

May 20, 2021, 12:29 AM	#5
Shadow9mm Senior Member Join Date: March 21, 2012 Location: Indianapolis, IN Posts: 4,603	So one question. How did you set your seating depth? Is it possible it just needs to be tuned a bit with this new bullet to get into a good spot in the barrels harmonic? After I test for powder load consistent I generally work back from the lands in 0.003 increments to find the best harmonic point in the barrel. __________________ I don't believe in "range fodder" that is why I reload.

May 20, 2021, 06:00 AM	#6
hounddawg Senior Member Join Date: March 1, 2009 Posts: 4,232	Just pulling some #s outta my keister here but sort the bullets so you have all the ones measuring 1.000 1.001 1.002 into one box 1.003 1.004 1.005 in another 1.006 1.007 1.008 in a third box. Then you have 1000 bullets measuring plus or minus .001 of each other. Start with the shortest box set the seating depth for 1.001 and when you shoot all those, adjust seating depth out .003 for the next box etc etc or sell them on gunbroker and get your money back __________________ “How do I get to the next level?” Well, you get to the next level by being the first one on the range and the last one to leave.” – Jerry Miculek

May 19, 2021, 11:40 PM	#4
Colorado Redneck Senior Member Join Date: January 7, 2008 Location: Northeast Colorado Posts: 2,007	Kilo How many rounds down the tube on your 6.5? And have you measured bolt face to lands and compared to your starting measurement? I had a CZ in 222 Remington the lands were .4 inches farther from bolt face by the time I sold it. Had to chase the lands to keep accuracy. Just an idea, and I am not pretending to be a guru.

May 20, 2021, 06:23 AM	#7
jetinteriorguy Senior Member Join Date: April 28, 2013 Posts: 3,476	Another thought, you may have settled on a seating depth with a very small window for accuracy, it may be possible by going deeper you will discover a depth with a larger window to allow for these bullet variances.

May 20, 2021, 07:19 AM	#8
cdoc42 Senior Member Join Date: March 13, 2005 Location: Pennsylvania Posts: 1,772	Kilotanker, more than a few years ago I tried Barnes in my .270 and came across a recommendation from Barnes that the bullets should be seated no closer than 0.05" from the lands. No details. But I suspected the manufacturing process produced variations in the bullet base to ogive that lead to that recommendation.

May 20, 2021, 08:41 AM	#9
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	Some bullet companys mix bullets from different forming die setups and are not shaped identical. Ask them if they do. Last edited by Bart B.; May 20, 2021 at 08:56 AM.

May 20, 2021, 09:32 AM	#10
hounddawg Senior Member Join Date: March 1, 2009 Posts: 4,232	The 6.5 140gn Barnes MB's seated .025 off lands in my .260 and the 6mm 105 gn seated to magazine length in my 6 ARC both give me good results. At least as good as the Bergers of the same weight/caliber. On another forum there is a thread and it seems no one has had much luck with those 145's. Someone said they copper up the barrel bad also but I have never had any issues with the ones I have shot __________________ “How do I get to the next level?” Well, you get to the next level by being the first one on the range and the last one to leave.” – Jerry Miculek

May 20, 2021, 01:15 PM	#15
kilotanker22 Senior Member Join Date: October 14, 2012 Location: North Central, PA Posts: 2,127	I just got off of the phone with Barnes. They said that they do not mix bullets from different machines or lots. All of the bullets in a specific lot come from the same run on the same machine. That is at least pertaining to the bullet in question. __________________ “We do not seek peace in order to be at war, but we go to war that we may have peace. Be peaceful, therefore, in warring, so that you may vanquish those whom you war against, and bring them to the prosperity of peace. – St. Augustine

May 20, 2021, 01:31 PM	#16
hounddawg Senior Member Join Date: March 1, 2009 Posts: 4,232	just checked a bunch of Barnes 175 30 cal MB's and only had .001 difference between the 25 that I checked, but thanks for the heads up. Now I will check a sample from every box before loading them __________________ “How do I get to the next level?” Well, you get to the next level by being the first one on the range and the last one to leave.” – Jerry Miculek

May 20, 2021, 01:50 PM	#17
Brian Pfleuger Moderator Emeritus Join Date: June 25, 2008 Location: Austin, CO Posts: 19,694	The most obvious solution is to modify your seating plug (or purchase a die) so that it touches the bullet at the ogive. I generally use cheap, standard Lee seating dies and the seating plug always touches near the tip. I just drill them out to a size that's closer to ogive. __________________ https://ecommercearms.com I am the owner/operator! Ask me for custom prices! No sales tax outside CO!

May 20, 2021, 04:27 PM	#18
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	Let's hope Barnes changes lots if they adjust the bullet's pointing die that shapes the bullet ogive. Meanwhile, note the place on the bullet's ogive that touches the rifling is about .002" smaller than the bullet's diameter. Last edited by Bart B.; May 20, 2021 at 07:47 PM.

May 20, 2021, 10:21 PM	#20
kilotanker22 Senior Member Join Date: October 14, 2012 Location: North Central, PA Posts: 2,127	They wanted to know what lot they were from and the guy said he would call me back after he got the lot number from me. I emailed them a photo of the label when I got home from work today. They did not have a comment on the variance I saw, but the gentleman seemed to be surprised by my results. He said he will get to the bottom of it and contact me. __________________ “We do not seek peace in order to be at war, but we go to war that we may have peace. Be peaceful, therefore, in warring, so that you may vanquish those whom you war against, and bring them to the prosperity of peace. – St. Augustine

May 20, 2021, 10:23 PM	#21
kilotanker22 Senior Member Join Date: October 14, 2012 Location: North Central, PA Posts: 2,127	That is a good point Bart. One that I knew was true, but also a point that does not get thought about often. __________________ “We do not seek peace in order to be at war, but we go to war that we may have peace. Be peaceful, therefore, in warring, so that you may vanquish those whom you war against, and bring them to the prosperity of peace. – St. Augustine

May 21, 2021, 08:59 AM	#22
Mike / Tx Senior Member Join Date: April 9, 2000 Posts: 2,139	While I don't use as many as I used to, when I was running Barnes they were always on top of their game. I've spoken to their techs quit a fee times thru the years and they have always gotten back to me in a timely manner, if they didn't have the answer immediately. Nowadays I just don't have a need for as many as I used to, so generally use something a bit less expensive . __________________ LAter, Mike / TX

May 21, 2021, 11:24 AM	#23
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,743	Kilotanker22, Several things: First, I suspect Brian may have given you the answer. If I understand correctly, you switched to a longer bullet shape. If the nose of the bullet is hitting the seating die stem way up inside before the opening in the seating stem's recess makes contact with the ogive, you will get seating depth variation equal to overall bullet length variation, and with hollow point match bullets, that can easily be 0.008" or so (I've measured up to 0.015" length variation on 30 cal Sierra MatchKings). Pull the seating stem out and look to see that a bullet dropped into it can't wiggle side-to-side because the tip bottomed out before the mouth of the stem opening makes contact. Second, note that cartridges are pushed forward into any available headspace during firing. The Courtneys have measured ignition delays from the moment of firing pin impact to be between about a millisecond and a half to three milliseconds or so, IIRC. A forward cartridge velocity of just 1.7 inches per second will cover 0.002" of excess headspace in the time it takes for the powder pressure to start getting serious, and most rifle firing pins shove a case forward faster than that, especially when the primer backing out adds its thrust into the story. My point is, a rimless cartridge will have its shoulder pushed against the shoulder of the chamber as the case starts to expand and stick the body to the chamber. That means what is setting the bullet jump is not the CBTO, but the case shoulder-to-ogive distance. So if you want to check your bullet jump precisely, that's the number you want to measure. Only if your case head-to-shoulder measurements are exactly identical, will CBTO give you an identically accurate measurement to the shoulder-to-ogive measurement. Third, as Bart pointed out, the actual diameter at which the bullet contacts the throat is just ahead of the shoulder where the ogive begins to depart from the cylindrical bearing surface portion of the bullet profile. If you are using a Hornady caliper comparator rather than the RCBS Precision Mic, Sinclair makes nice stainless comparator inserts that are shaped to mimic a chamber throat and that contact the ogive way down there, unlike the aluminum Hornady inserts. These inserts fit the Hornady caliper adapters, so it is only the insert you want to upgrade if you don't have one already. Part #090264. Once you have that, you can use the Hornady case comparator insert to first check and record the head-to-shoulder measurement for each case. Then put the Sinclair insert in and get the head-to-ogive measurement with it. Subtract the first number from the second for each round. That will give you the actual bullet jump variation. If your seating stem does leave the usual ring mark from properly contacting the ogive, put a comparator insert (brand doesn't matter here) into your caliper adapter that meets the bullet where the seating stem does. Measure a bunch of your bullet base-to-ogive with that insert and again with the Sinclair insert and see how much the difference varies. That will give you the contribution ogive shape inconsistency contributes to your jump. Finally, note that if your seating stem is contacting the bullet ogive properly, any extra distance to the bullet base from the ogive will simply be pushed that much deeper into the case neck during seating. It should not affect bullet jump the way seating from tip contact with the bottom of the seating stem will, as long as the ogive contour coming off the bearing surface is consistent. That last test I mentioned will determine that. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

May 21, 2021, 11:44 AM	#24
kilotanker22 Senior Member Join Date: October 14, 2012 Location: North Central, PA Posts: 2,127	Thanks Unclenick, I will double heck for these things this weekend when I am off work. __________________ “We do not seek peace in order to be at war, but we go to war that we may have peace. Be peaceful, therefore, in warring, so that you may vanquish those whom you war against, and bring them to the prosperity of peace. – St. Augustine

May 21, 2021, 05:52 PM	#25
Rimfire5 Senior Member Join Date: January 2, 2009 Location: Northern Virginia Posts: 982	kilotanker22, I think Unclenick has given you the answer. That said, I measure cartridge base to ogive on every round I load and I have never seen that amount of variation on loaded rounds and I have loaded over 53,000 rounds with all kinds of bullets. Also, having purposely varied the jump on different loads to optimize the jump for a particular bullet, my results show that a change of 0.008 in effective jump is not catastrophic enough to change the average group size by 0.7 inches at 100 yards. It might change the average group size by 0.050 to 0.1 but never 7 times that. Even massive velocity changes don't make that much difference in group sizes from a barrel that shoots 0.25 to 0.3 inch groups. I suspect that there might be a factor other than jump at play to create that amount of growth in average group size.