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Old April 4, 2007, 08:20 PM   #26
Bullet94
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dirty habit
The measurement i was on about was from the base of the cartridge to the ogive, from what i can figure, this overall measurement should be the same with any bullet i use, although granted, ill have to change the seating die each time.

I think you have it right. If you measure from the bolt face to the start of the lands in your rifle. You really are measuring a fixed distance because you are measuring your rifle (this distance will remain the same unless barrel erosion changes it). Now when you measure cartridges from the base of the case to the part of the bullet that contacts the lands, the distance will remain the same using different shaped bullets because, the only part of the bullet to contact the lands will be the part of the bullet that is that diameter. But since you can’t measure from there you use a comparator which contacts the bullet at a different place on the ogive. Your seating die will contact the bullets ogive in still another place. The comparator and the seating die will be at different distances from the place where the bullet contacts the lands depending on bullet shape hence the different measurements when measuring with a comparator and the reason you have to adjust your seating die when changing bullet shape. This can also be confusing because some people refer to the part of the bullet that contacts the lands as the (ogive) and SAAMI says the (ogive) is the curved portion of a bullet forward of the bearing surface.
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Old April 4, 2007, 11:18 PM   #27
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Mrawesome22, yeah thats right, i think i may not have explained myself too well earlier. The measurement i was on about was from the base of the cartridge to the ogive, from what i can figure, this overall measurement should be the same with any bullet i use

Ahhhhh, I think I see what you mean now. Yes, if you adjust your seating die to put every different bullets ogive in the same place, and measure from base to ogive, you will come up with the exact same measurement. As long as each case has the same dimensions.

And think about this. Poor head space (a.k.a. a lot of room between bolt face and case head) will cause the ogive of your bullet to be farther or closer to the rifling by moving the rifle up or down. But neck sizing fire formed brass eliminates this. Again I recommend the Lee Collet Neck die.
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Old April 6, 2007, 02:47 PM   #28
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Let me see if understand what you guys are thinking. The base of the case to the ogive should be the same with every bullet you load, you'll just have to adjust the seating die to get the same overall length, base to ogive?

But if you make every bullet 2.326" from base to ogive, they will all be a different distance from the rifling. For example, these are actual measurements for each bullet so that they are all 0.015" from the rifling in my .270 WSM:

130gr bullets: Remington 2.347"
Hornady SST 2.245"
Speer 2.277"
Nosler Bal Tip 2.293"

140gr bullets: Hornady SST 2.382"
Nosler Bal Tip 2.301"
Sierra HP 2.296"

So, for example, if you made the Remington 130gr and the Hornady SST the same OAL, base to ogive, of 2.347", the Remington would be 0.015" from the rifling and the Hornady would be longer from ogive to rifling and would actually be 0.008" away.

The base of the case to the rifling in your rifle is the same, yes. But the position of the ogive on every bullet is different.
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Old April 6, 2007, 05:23 PM   #29
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cdoc, i might be using the wrong term but what I mean by ogive is the last bit of forward curve before it becomes the bearing surface, the "transition" part of the bullet i suppose you could call it?
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Old April 6, 2007, 11:03 PM   #30
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You're right. The ogive is where .224" becomes smaller.
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Old April 6, 2007, 11:42 PM   #31
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Quote:
Chambers: that all-important point where everything starts
Guns Magazine, Sept, 2005 by Glen Zediker


So I don't leave anything out, I'm going to start this off pretending nobody knows nothin'. A rifle chamber is a hole cut in the breech end of a barrel so a round of ammunition will fit. It's a lathe operation. A "chamber reamer" is the tool that cuts this hole and it is shaped the same as a cartridge case with at least part of a bullet stuck in it. The reamer is going to cut out the case body and shoulder silhouette, the case neck, and then extend into the bore to form a bullet profile silhouette. It's here, the bullet profile area, where major tooling differences exist. There are a lot of different .223 Remington reainers. The two most commonly used in factory-done guns are at opposite ends of this universe--one is the shortest, and one is the longest.
Let's look closer. What I called the "bullet profile area" is technically called a "leade." We can also call it the "throat." Inside the chamber, the distance between the end of the case neck and the first point cut into the rifled portion of the barrel coinciding with the barrel's land (rifling) diameter is the preeminent variable determined by the reamer. Land diameter will be the smallest dimension inside a bore. If the first point of full land diameter (usually 0.219" in a 224-caliber barrel) is farther from the end of the case neck (farther into the bore), then the chamber has a longer leade or throat. The bullet won't contact the lands until, of course, it reaches the point on the bullet that coincides with land diameter. I call this the first point of "major diameter" on a bullet. The effect or influence of this conical space ahead of the case neck is simple: The more space the less pressure, and the more space, the farther the bullet must "jump" until the bullet contacts the lands. Read all that again.

From above -
Land diameter will be the smallest dimension inside a bore. If the first point of full land diameter (usually 0.219" in a 224-caliber barrel) is farther from the end of the case neck (farther into the bore), then the chamber has a longer leade or throat. The bullet won't contact the lands until, of course, it reaches the point on the bullet that coincides with land diameter. I call this the first point of "major diameter" on a bullet.


If I understand this right the distance from the bolt face to the land diameter is fixed. The OAL measured at the land diameter will be the same regardless of a bullets weight, length or shape.
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Last edited by Bullet94; April 7, 2007 at 09:11 AM.
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Old April 7, 2007, 09:07 AM   #32
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Aold timer once told me quote

In reloading never assume anything once and measure everthing twice.
and reloading is not for anyone looking for shortcuts

he was also our range safty officer.
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Old April 8, 2007, 10:32 PM   #33
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For factory rifles this is a tempest in a teapot.

If you want to ensure true uniformity of your cartridges for a match rifle then you should first cull cases based on the actual capacity. This assumes you have sized and trimmed them all to the same body diameter, shoulder to base length and neck trim length also called trim length, not overall length.

Then you must cull bullets, first by weight, then by the base to ogive length. I like the Sinclair bullet comparator for this as, they say it is actually reamed with the same type reamer used in making custom chambers, rather than just drilled and chamfered to an arbitrary measurement like the Hornady (formerly Stoney Point) tool. At this point, if you are shooting at 300 yards or so, you might trim the meplat to ensure uniform ballistic coefficients of all bullets. Using a comparator to only check the COAL without doing the above is like changing your car's oil and not the filter.

By doing all this you ensure that you have produced a uniform cartridge both inside and out. Did I forget to mention checking concentricity? Well, no matter. That's another subject.
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Old April 9, 2007, 04:43 PM   #34
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It is gratifying to see so much interest in this topic. With enough heads invested, we are more likely to see some useful idea appear that the rest of us can “borrow”.

Some of the discussion seems to have talked itself around the circle to confusing chamber headspace with cartridge headspace. It occurs to me it may be beneficial to go over some terminology, so everyone is speaking on the same page. First, the bullet parts, with small additions, as defined in Robert A. Rinker’s, Understanding Firearm Ballistics:



The main objective is bullet alignment with the bore. Bullet seating depth tools, like case prep tools and lot of other reloading techniques for extreme accuracy, were largely pioneered for benchrest shooting. Benchrest shooters invariably neck size only! After firing about three times, such cases pretty much stop springing back and truly fill the chamber. This means a firing pin will not move it when it is fired. So, measuring from the base of the case to the beginning of the ogive, just beyond the bullet shoulder, where it contacts the rifling start in the throat, will produce consistent results.

It is when you resize a case, or use new, unfired brass that the trouble starts. For example, commercial .308 brass is typically 0.002” to 0.003” under S.A.M.M.I. minimum chamber headspace. The spec actually allows it to be 0.002” over the chamber minimum headspace because the chambers are specified 0.011” wider than the cases. A long case can therefore be jammed in by the bolt and squeezes out wider to compensate. Indeed, page 244 of Hatcher’s Notebook contains information that a rapidly worked bolt (manual) can shorten a case 0.006”, deforming it out into that extra width. Even a resized case whose shoulder has been pushed back only 0.002” will be subject to this problem, because the sizing die also made the case narrower than the chamber. So, working a bolt slowly is required to maintain critical bullet position off the lands, too.

Below is an illustration of the normal firing sequence with a fully sized case. I made the first illustration with a gap ahead of the shoulder to represent the difference in cartridge and chamber headspace. When the firing pin goes forward, it pushes the bullet with it by whatever extra space is there. If you had also worked the bolt fast (or are using a self-loader) this error will have grown upon chambering. Thus, when the firing pin strikes, the case and bullet will move forward until they are either stopped by the shoulder or the extractor hook stops it. This latter symptom occurs commonly in 1911 pistols and seriously deteriorates the accuracy of cast bullets. Jacketed bullets realign themselves enough so you can’t tell in a handgun, but in a rifle it can cause groups to open up an m.o.a. or more.




This image illustrates the possible measuring error in cartridges whose cases have different headspace at the shoulder:



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Old April 9, 2007, 08:41 PM   #35
Bullet94
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Unclenick
Thanks, I really like the bullet parts picture don’t think I’d seen that before. The part about headspace was informative as well.
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Old April 13, 2007, 09:15 AM   #36
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I should add one for case parts and put the two together. This is a link to the Redding tool mentioned in the last illustration above. It correctly measures the bullet seating depth from the shoulder of a rimless case to the bullet ogive.

http://www.redding-reloading.com/pages/instantind.html

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Old April 13, 2007, 01:51 PM   #37
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Unclenik, great post!!!!

The only thing I reaise a question about is the drawing of the bullet shows the ogive and shoulder being two different areas on the bullet. OK so far.
But the drawing of the cartridge where it talks about the Redding tool has a line called "ogive" on the bullet where the "shoulder" is on the other drawing.

I gather from the first drawing that the ogive is not that portion of the bullet where the bullet engages the rifling. It should be the "shoulder." Yes? No?
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Old April 13, 2007, 08:50 PM   #38
Bullet94
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cdoc42

From above –

Quote:
Unclenick
So, measuring from the base of the case to the beginning of the ogive, just beyond the bullet shoulder, where it contacts the rifling start in the throat, will produce consistent results.
Looks to me like the shoulder is where the ogive and the bearing surface meet.
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