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Old October 3, 2019, 11:53 AM   #26
Don Fischer
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I don't know this for a fact as I don't give a hoot but, I've read that each bullet by itself may be a different length and that way the ogive might move. The ogive, or what ever you want to call it, should always be the same size. The bullet will be stopped by the ogive every time at the lands. I have taken and figured out my OLL with a cleaning rod and bullet and used it to set OLL. Guess what, sometime's even though the die is never readjusted, the die must be adjusted to keep a round or two off the lands. Tells me the ogive has for some reason moved I think!
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Old October 3, 2019, 01:16 PM   #27
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whatever Bart, I could post a half dozen or more targets that show the same phenomena but why bother. I hope this doesn't get this doesn't get your undies in a twist but I will take Tony Boyers word over yours every day of the week. Especially since I have seen it in action with my own eyes

@ Don Fischer. Last evening this thread and another over at Accurate Shooter got me interested in my bullet seating depth consistency is I did some measuring.

First I checked 75 .223's loaded with a light charge of Varget in Lapua brass with 77 SMK's. There were 75 of them and I was shocked at the inconsistency. I was plus or minus .005 from the target BTO. These were loaded last Friday using a arbor press and a Wilson die. After reseating all 75 I remeasured and the differences had dropped to plus or minus .001.

Today shooting from a bench with a bipod and rear bag I shot 6 groups at 200 yards and the smallest was .5 MOA and the largest .8 MOA using that ammo.

Next I checked thirty 6.0 Creedmoor rounds that I had left over from a loading session last April. Alpha brass, 107 SMK and medium hot load of H4350. Only 5 out of 40 was more than plus or minus .001 from the intended length and for some reason gave me a fight to get them back into specs. I suspect a doughnut in the neck but they will all get a neck reeaming before next loading. I shot 4 groups of 5 shots at 800 yards and all averaged less than 1 MOA. It was a light wind but 94 F and sunny so the mirage was kicking. For my ability level I will take 1 MOA if I could get them centered over the X, which is my major challenge in this game
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Old October 3, 2019, 02:05 PM   #28
Bart B.
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Originally Posted by hounddawg View Post
whatever Bart, I could post a half dozen or more targets that show the same phenomena but why bother. I hope this doesn't get this doesn't get your undies in a twist but I will take Tony Boyers word over yours every day of the week. Especially since I have seen it in action with my own eyes
And cartridges lay in the chamber bottom when fired.
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Old October 3, 2019, 02:37 PM   #29
old roper
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This is from SAAMI Spec.

OGIVE

The curved portion of a bullet forward of the bearing surface.

OGIVE BULLET

The curved forward part of a bullet.
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Old October 3, 2019, 02:53 PM   #30
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This is from SAAMI Spec.

OGIVE

The curved portion of a bullet forward of the bearing surface.
OK, so we have SAAMI, and the bullet makers, and generations of industry use all using the term "ogive" to refer to a portion, or a section of the bullet. It is an area, not a point.

People who are measuring "to the ogive" are measuring to a point, somewhere on the ogive.

I understand the desire for precision, but for that precision you need a precise term, (which "ogive" is not), a term that is not in use for some other definition.
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Old October 3, 2019, 03:07 PM   #31
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I understand the desire for precision, but for that precision you need a precise term, (which "ogive" is not), a term that is not in use for some other definition.
I agree.

Read the last two paragraphs in my post #13.

It's a "ogive datum diameter" thing that is relevant to only the specific barrel and bullet used. May change with throat wear.

It's related to the distance that a bullet travels from its seated position in the cartridge case to its initial engagement of the rifling. SAAMI calls that distance "bullet jump."

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Old October 3, 2019, 03:42 PM   #32
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44AMP, I think I understand your position, but, then, what term do you suggest should be used when we all speak about seating the bullet some distance from the lands/leade/rifling? What part of the bullet should be described when a comparator device of the proper caliber diameter, attached to one's caliper, is used in this exercise?
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Old October 3, 2019, 03:46 PM   #33
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Don Fischer said: " Guess what, sometime's even though the die is never readjusted, the die must be adjusted to keep a round or two off the lands. Tells me the ogive has for some reason moved I think!"

I have had that experience as well and found the problem to be primers that were not adequately seated. If I have a round that doesn't match my OAL-to-the-"ogive" I stand the round on the benchtop and found it rocks. I gently reseat the primer and the repeat measurement is where I expected it to be.
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Old October 3, 2019, 04:41 PM   #34
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well cdoc, part of my loading routine is checking every primer for seating depth so that would not account for the differences I saw last eve. And it would have been impossible to fix a high primer using a Wilson in line die with the base.
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Old October 3, 2019, 05:00 PM   #35
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well cdoc, part of my loading routine is checking every primer for seating depth so that would not account for the differences I saw last eve. And it would have been impossible to fix a high primer using a Wilson in line die with the base.
Flip the base upside down then use the seater off center on the base bottom.

I've done that with mine.
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Old October 3, 2019, 06:47 PM   #36
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I check each primers seating depth while seating with a dial indicator as I return it to the bin. I am suspecting the guy pulling the handle on the press was the culprit and was sloppy applying pressure with the arbor press when loading. I had 75 loads to measure and got in a hurry most likely. Loads were 3 days old and never left a climate controlled room with .003 neck tension. I will probably go back to using my regular press instead of the arbor unless I lose my mind over this stuff and buy a 21st century hydro seater
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Old October 3, 2019, 07:04 PM   #37
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If I understand you correctly, hounddawg, you have eliminated elevated primers as the cause of variations in seating depth, as measured with a vernier caliper and comparator of proper caliber diameter.

Let's be sure we're talking about bullets of a given weight from the same manufacturer, out of the same lot number box. What might occur that causes a difference in measurement from one seated bullet to the next?

1) A manufacturing change in the position of "the curved portion of a bullet forward of the bearing surface," as measured with a comparator of proper caliber diameter? (or, "ogive" for lack of a better term)
2) Variation in measuring technique by the reloader, i.e., applying more or less pressure on the caliper per cartridge?
3) The die worked loose between measurements?

Any other thoughts?
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Old October 3, 2019, 07:38 PM   #38
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what term do you suggest should be used when we all speak about seating the bullet some distance from the lands/leade/rifling?
I thought a bit, perhaps "engagement point"?? What we're talking about here is the point on the ogive where it touches the rifling (engages the rifling) when it is far enough forward.

The term would be consistent, always referring to the point on the bullet where the diameter of the bullet touches the rifling, but understanding that the location of that point on the bullet will be in a slightly different place with each different bullet style and each different barrel.

I'll be honest and admit I don't use a comparator, nothing I do with my guns and ammo requires that degree of precision. From what I've read on the forum, comparators seem to cause more confusion than precision, though its quite likely that the guys who do get a benefit from using them simply don't write about it...

Here's something else that occurred to me, similar to the "engagement point" of the rifling on the bullet, its the "engagement point" of the bullet seating stem on the bullet.
Same in principle as the bullet touching the rifling but happening on the nose of the bullet, close to the tip. If you are getting variations measuring to the engagement point of the rifling on your loaded ammo, might not the variations be the result of variation of the seating stem "engaging" the bullet during seating??

Using the same seating stem adjustment, one will get different over all lengths with different ogive profile bullets, easily seen if loading something
like .30 cal 150gr spitzer, spire point and round nose bullets.

thoughts?
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Old October 3, 2019, 09:32 PM   #39
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I'm not aware of any bullet seater stem whose bullet engagement point contact diameter is even close to where the lands in the throat will first touch the bullet. That's usually a few thousandths less than bullet diameter.

Measure a seater stem's bullet "contact datum diameter." If it's smaller than the barrel's bore diameter, that point will never touch the rifling; anywhere.

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Old October 3, 2019, 10:58 PM   #40
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If I understand you correctly, hounddawg, you have eliminated elevated primers as the cause of variations in seating depth, as measured with a vernier caliper and comparator of proper caliber diameter.

Let's be sure we're talking about bullets of a given weight from the same manufacturer, out of the same lot number box. What might occur that causes a difference in measurement from one seated bullet to the next?

Starrett 25-141 dial indicator. It's spindle is .018 smaller than a small primer. Makes depth checking simple. The bullets were from a 500 round box

Pretty simple to figure out that if reseating cured the problem they were not seated correctly the first time.
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Old October 4, 2019, 10:30 AM   #41
Don Fischer
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Originally Posted by cdoc42 View Post
Don Fischer said: " Guess what, sometime's even though the die is never readjusted, the die must be adjusted to keep a round or two off the lands. Tells me the ogive has for some reason moved I think!"

I have had that experience as well and found the problem to be primers that were not adequately seated. If I have a round that doesn't match my OAL-to-the-"ogive" I stand the round on the benchtop and found it rocks. I gently reseat the primer and the repeat measurement is where I expected it to be.
I got to where over the years I seldom have to stand a case on a flat surface to see if a primer is seated enough. In the beginning, I found a lot of them not quite deep enough even though they seem to be.
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Old October 4, 2019, 11:06 AM   #42
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Hollow point bullet jackets are made much the same way as cartridge cases. They've got shape dimension tolerances. When a lead core is pressed into the open end of the jacket then a pointing die shapes the ogive, it too, will have shape dimension tolerances.

Twist gently a bullet ojive in the muzzle of a barrel. Measure the distance from its mark to the bullet's base then to its tip. Repeat this with 9 more bullets recording each dimension. Note the spread of each.

Now twist each bullet ogive in the seater stem. Measure the stem mark to muzzle mark then record the numbers for each bullet. Note the spread.
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Old October 4, 2019, 01:33 PM   #43
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best tool I have found for checking primer pocket depth and seating depth. Lots of used ones in good shape. Mine was given to me by a guy who has retired and had 4 or 5 in his garage/home shop. Just unscrew the contact from the spindle and it is the perfect diameter. Mine is so old the face is yellow so I guess it is vintage

Starrett 25-141 Ebay
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Old October 4, 2019, 02:06 PM   #44
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Bart B. That small group you posted is over 20yrs old. Do you have anything current.

This is from your old site.

https://groups.google.com/forum/?fro...ns/iL7zv-cktJc
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Old October 4, 2019, 02:32 PM   #45
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SAAMI also defines the throat:

Quote:
Originally Posted by SAAMI
THROAT

The tapered portion of the bore of a barrel, immediately ahead of the chamber which is sized to provide clearance for the bullet of the loaded cartridge. Also referred to as Leade or Ball Seat and is associated with Free Bore...
SAAMI is a concensus standards organization, so that will be the definition the industry accepts. Just as the tapered shoulder portion of a chamber is where a rimless bottleneck cartridge seats, so is the throat where the bullet seats if you load for zero bullet jump.

Cdoc42,

I think you will find two factors can cause a pressure difference. One is that your longer ogive bullet leaves more powder space under it, and that tends to lower pressure a little. Second is that a longer ogive radius means, when bullet jump is the same, that the annular ring is a little smaller, so less gas bypass can occur during the time it takes to get to the throat. These two influences tend to be oppositely directed, so they tend to cancel, but they won't have the same significance, so they won't do it perfectly. This will result in slightly different barrel times and exiting at a different point in the barrel flexure from firing could account for the POI shift you mention.

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Old October 4, 2019, 03:14 PM   #46
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Bart B. That small group you posted is over 20yrs old. Do you have anything current.

This is from your old site.

https://groups.google.com/forum/?fro...ns/iL7zv-cktJc
I am just amazed that anyone could shoot a group like that 20 years ago before the days of induction annealing and other high tech doo dads.
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Old October 4, 2019, 04:30 PM   #47
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I am just amazed that anyone could shoot a group like that 20 years ago before the days of induction annealing and other high tech doo dads.
Mid Tompkins shot forty Lapua 185 gr. FMJRB bullets from his Hart barreled 308 Win M70 match rifle that went inside 2 inches at 600 yards back in 1971. Some 10 shot groups were under an inch.

The quality of centerfire barrels and bullets has improved little over the last several decades.

22 rimfire match ammo quality declined in the early 1980's. 100 yard prone 40-shot any sight records set before then still stand, as do some at 50 yards. Barrel life is now half that possible back then.

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Old October 4, 2019, 05:36 PM   #48
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The quality of centerfire barrels and bullets has improved little over the last several decades.
the gear is only half the equation
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Old October 4, 2019, 06:03 PM   #49
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the gear is only half the equation
I think gear is only a third or a fourth of the equation.
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Old October 4, 2019, 07:07 PM   #50
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My theory is gear, ammo, shooter's physical technique, endurance and experience level, oh add in a good dose of outhouse luck for the occasional holy <insert 4 letter word of choice here> ! group
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