kilotanker22
New member
That is a good point Bart. One that I knew was true, but also a point that does not get thought about often.
Interesting Find, Bullet Base to Ogive...
- Thread starter kilotanker22
- Start date
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 .
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 .
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.
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
New member
Thanks Unclenick, I will double heck for these things this weekend when I am off work.
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.
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.
kilotanker22
New member
I checked the seating stem. The die I am using is the Forster Bench rest die. The depth on the inside of the seating stem is .950". The Ogive radius, (from bearing surface of bullet to tip) is approximately .750". Where the stem contacts the Ogive is forward of the bearing surface by a little way. I think it is safe to say that I am not seating from the tip.
However I did find something else. Inside of the seating stem there looked like a small burr or another piece of some sort of metal. I used my VLD chamfer tool and a cleaning brush to remove it.
I will test this again later when I have time to load ammo
However I did find something else. Inside of the seating stem there looked like a small burr or another piece of some sort of metal. I used my VLD chamfer tool and a cleaning brush to remove it.
I will test this again later when I have time to load ammo
lll Otto lll
New member
If I wasn't happy with a bullet....I wouldn't use it. It's as simple as that.
If I suspected the bullets were out of spec, I'd return them.
If I suspected the bullets were out of spec, I'd return them.
Don't forget, he had good results with it initially. That's why he bought a pile of them. The trick is figuring out what's different now. If the point is not bottoming out in the seating stem, the next thing I would do is use the seating stem as the comparator bushing and measure cartridges with it and the caliper to see if the base-to-seating-stem contact distance is consistent.
kilotanker22
New member
That is a great Idea Unclenick. I will definitely try that
kilotanker22
New member
So after Cleaning that seating stem (chamfering and degreasing), My problem seems to have resolved itself.
While loading some ammunition this week I saw less than .001" variation in my CBTO measurement. I measured all 50 of the cartridges I loaded.
Unclenick was correct that the bullet base to ogive variation wouldn't matter and would simply be pushed into the case during the seating operation.
The following is a group fired this morning using the same lot of 50 bullets that had the variations in my opening post. I shot ten, three shot groups that look just like this one. This is the only one I measured cause I had to get to work and did not have a great deal of time.
These results make me wonder if whatever was in that seating stem was throwing off my concentricity and that was the cause for going from .25-.3 moa up to 1 moa?
While loading some ammunition this week I saw less than .001" variation in my CBTO measurement. I measured all 50 of the cartridges I loaded.
Unclenick was correct that the bullet base to ogive variation wouldn't matter and would simply be pushed into the case during the seating operation.
The following is a group fired this morning using the same lot of 50 bullets that had the variations in my opening post. I shot ten, three shot groups that look just like this one. This is the only one I measured cause I had to get to work and did not have a great deal of time.
These results make me wonder if whatever was in that seating stem was throwing off my concentricity and that was the cause for going from .25-.3 moa up to 1 moa?
Attachments
interesting. After reading this I took my Frankford Armory seater and used a bit of hot glue to stick a piece of brass shaving into one of the seating stems to try and duplicate your theory. With ten dummy rounds it caused the base to meplat measurements of the loaded rounds to be off by .001 - .002. After pulling, the bullets base to meplats turned out to be off by .001 - .002 which leads me to believe that the seating stem was hitting the meplat rather than the ogive of the bullet. Concentricity was not affected at all however, and all ten measured within .0015 or less.
Nice three shot group however, and it is good that someone can get those 145's to group
kilotanker22
New member
Interesting. I really do not know what my problem was now. I guess it is possible that there is something I have over looked. I did take the die apart and clean the entire die when I removed the seating stem. After which the problem went away. I will continue to check for that problem and see if it returns. If so, maybe I can find the cause.
kilotanker22
New member
I have had the best results close to the lands with this bullet. I have had excellent results with Hodgdon's published max load for the 147 grain ELDM and H-4350. That load seems to shoot every bullet from 140-150 grains very well in every Creedmoor rifle I have tried it in. This includes two of my own rifles and a dozen or so other rifles. Barrel lengths from 20-26 inches.
from your first post, .008 is enough to cause major grouping issues
my guess, and the key word there is guess, is that the dirty seater was seating off the ogive and the gunk was shifting or maybe the lock ring not tight enough or something else was causing this.
Anyway grats on getting it straightened out. Post some pics of some 5 - 10 shot groups at longer ranges when and if you can. I like Barnes myself and had good luck so far with the 6.5/140's and 6mm 107's but you are the first to post good things about the 145's. What velocities are they liking?
kilotanker22
New member
I am launching these at average velocity of 2796, ES 20, SD 5.8. That is from a 15 round string I shot the other day when playing with my new tuner brake.
Edit: I am using CCI 450 primers and Lapua brass
Edit: I am using CCI 450 primers and Lapua brass
kilotanker22
New member
I will get some 10 shot groups in this weekend if I can find the time. Where I shoot is always windy and limited to 300 yards. I will get groups at 100 and 300 yards.
Larger groups are important if you record the location of every single bullet hole. Then you can use Excel or a calculator and a piece of paper to work out the center and radial standard deviation numbers. However, if you measure group diameter as in the photo, there is a point at seven shots, beyond which increasing the number of shots increases the likelihood of getting an outlier more than it increases the "typicalness" of the group, skewing the results. To get the most information from group diameters in the fewest total shots, fire six or more seven-shot groups and average their diameters. Five shot groups also work pretty well for this, but you want at least ten of them. The explanation for all this is in this article.
Congrats on getting the issue resolved. I wish we could go back and compare the troublesome loads with the good ones via every possible measurement. However, since cleaning the die helped, you've found out that oil and factory dirt or other contaminants can mess with a precision seating die. I've had that experience with a Redding Competition Seating Die. My .308 Win copy didn't seat particularly better than any other die until one day I pulled it all apart, soaked its parts in Naphtha, dried them, and then put a super-thin lubricating layer on the (Sprinco Plate+ Silver). After that, everything I seated with it had half a thousandth runout or less as long as the case walls weren't grossly uneven in thickness at the neck.
Congrats on getting the issue resolved. I wish we could go back and compare the troublesome loads with the good ones via every possible measurement. However, since cleaning the die helped, you've found out that oil and factory dirt or other contaminants can mess with a precision seating die. I've had that experience with a Redding Competition Seating Die. My .308 Win copy didn't seat particularly better than any other die until one day I pulled it all apart, soaked its parts in Naphtha, dried them, and then put a super-thin lubricating layer on the (Sprinco Plate+ Silver). After that, everything I seated with it had half a thousandth runout or less as long as the case walls weren't grossly uneven in thickness at the neck.
Statistically that is true Nick but math seldom tells the whole story. For some shooters getting a 9 after 19 X's and 10's is the outlier, for others like myself getting a 8 after 19 X's, 10's and 9's is the outlier
@ Kilo what I look for when practicing in windy conditions is the vertical spread and the horizontal. Vertical will tell me what the load/barrel is doing and the horizontal is telling me how good my wind reading was or was not. Windy at 300 is perfect for practice in my opinion. The best evaluator of the rifle and the wind reading ability of the person pulling the trigger.
When I look at pics of a lot of my targets and it aint real hard to figure out which way the wind was blowing. Vertical spreads of .5 and .6 with horizontals of a MOA or better. I have pic of a 300 match target that has a 1 inch vertical spread and 4.5 inches horizontal. LOL
. Twenty shots that look like a ribbon laid across the target. I am not real proud of that target but I keep it as reminder that it wasn't the rifle or the ammo that screwed up that day.That is why I don't worry about buying that $5K custom or improving my ammo any until I learn to read the wind better. A BAT action, AMP annealer, $2.5 K neck turning machine and a Labradar would not help me read that wind one bit better
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kilotanker22
New member
I did shoot this again yesterday. I did not have a great deal of time so I just fired a 20 shot string. The barrel was already a little warm. Before I shot the 20 shot string, I had to sight in the optic (switched optic from different gun). Took maybe 6 or 7 shots to sight in without a bore scope.
Anyway, the group turned out alright as far as I am concerned. The group measures 1.011: outside to outside. Subtract .264" to get .747". Divide by 1.047" to get .71 MOA for a 20 shot group. That was from a bipod and rear bag with a warm barrel. I am happy with that. the attached image is the 20 shot group.
Anyway, the group turned out alright as far as I am concerned. The group measures 1.011: outside to outside. Subtract .264" to get .747". Divide by 1.047" to get .71 MOA for a 20 shot group. That was from a bipod and rear bag with a warm barrel. I am happy with that. the attached image is the 20 shot group.
