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Thread: COAL, Ogive, Bullet Comparators and Advil...

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    Moderator LuJon's Avatar
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    Default COAL, Ogive, Bullet Comparators and Advil...

    OK, I have been watching vids and reading up on this and it seems that everyone does things their own way.... It seems that one could use one of the various COAL gauges either home made or commercial and get the COAL using ANY bullet. Once they have that done then using a bullet comparator gauge like the one from Sinclaires to find the Ogive you should be able to find the cartridge length to the Ogive for your rifle.

    Once you know the COAL measured to the Ogive for your rifle it seems like there would be no need to test each different bullet in the rifle with the COAL gauge. Can't you just load any new bullet to the same COAL measured to the Ogive?

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    Member Smokey's Avatar
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    LuJon,
    It can cause migraines for sure!
    As you change bullets the Ogive ( or shape of forward portion of bullet) changes which in turn will allow you to seat bullets either deeper into the case or out further depending on that shape. So, the only way I can see to get one recipe is to follow the SAMMI guide number for that caliber as I think they take into account the worst case scenario and give the reloader some "wiggle room"...
    However, if your looking for ultimate accuracy that may not be the optimum length....
    Perhaps someone with more knowledge can explain it better than I ???
    When asked what state I live in I say "The State of Confusion", better known as IL....

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    Lujon...I'm thinking "maybe" to your question.

    I think the key to your logic is that you start by obtaining an accurate measurement of the distance to the lands for that particular rifle and a specific bullet, then mathmaticly adjust those measurements to a different bullet in that same rifle, i.e., derive an adjusted COAL by computing the differential between the distance from the bullet tip to the Ogive of the originally measured bullet and the distance from the tip to the Ogive of the new bullet.

    You can't simply rely on SAMMI specs because not all chamber throats are cut EXACTLY the same from one manufacturer to another. Granted, the variance may be slight in some cases, but not always. As just one example, I loaded some 375H&H for a friend of mine's Sako and his distance to the lands was significantly different than mine for the same bullet. I'm sure some others on this forum have had similar experiences.

    It's all about how precise you want to be. Some handloaders are driven to obtain maximum accuracy; some are just looking to cut the costs of ammunition and get a 2" MOA for their hunting rifles, and some are happy with minute of car door at 50yds. I fall into the first category and get too fussy sometimes, but it's my nature. I sure don't think I have any more knowledge than anyone else here.

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    Quote Originally Posted by LuJon View Post
    Once you know the COAL measured to the Ogive for your rifle it seems like there would be no need to test each different bullet in the rifle with the COAL gauge. Can't you just load any new bullet to the same COAL measured to the Ogive?
    Assuming that you mean the distance from the case head to the contact spot on the bullet that touches the lands and not the head to the tip of the bullet your answer is yes.

    For example, with the system I use for a .308 bore my tool head is .300 in diameter. Measuring from the head to the spot that contacts that diameter on the bullet, (simulating barrel bore to ogive contact) that distance is the same but the COAL will be different on most bullet designs measured.

    A round nose bullet will have a shorter COAL than a pointed bullet but the tool measures the distance from the head to the contact spot or ogive. That contact distance will be the same on both bullets but the COAL will be very different.

    In that example if you want to load to .025 off the lands the tool will allow you to establish that distance without regard to COAL.

    COAL is important if your desire is to load from a magazine. If your limited to a max length for feed function then the tool will tell you how far you are from the lands at the COAL length in case you want that number for a reference.

    I hope that helps...

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    Moderator LuJon's Avatar
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    Thanks!

    Marshal, you are correct that I was referring to the length from the case head to the ogive.

    I finally found a decent vid showing the steps pretty clearly as well.


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    What I have a hard time with is getting that exact Ogive measurement several times in a row. I do it over and over, with both the dowel rod method, and the Hornady OAL Gauge method, and seems they don't come out exactly the same enough times to rely on.

    By this video he mentions, "Don't push the bullet in too far or it will jam into the lands and you'll get a misread."
    That's probably my problem, making it just "Kiss the lands" and getting a measurement there.

    Any ideas guys on how to do this better?
    With the dowel rod method, I slide a bullet into my modified Hornady case so it will line up correctly, insert the "Dummy Cartridge" carefully until the bullet feels tight against the lands, then retract the case, this always leaves the bullet slightly stuck against the lands (needing to be removed by a dowel rod from barrel end, just a slight tap,)
    after I get that measurement, then close the bolt and get another read on the same Dowel rod. Seems so foolproof except for the marking of the rod, ( I do that with a razor blade, it seems exact enough)

    Yet somehow I rarely get the same exact measurement three times in a row. Yeah I'm probably to much of a perfectionist but I'd like to get it just dialed in perfectly. When were talking .02-.05 "Off the Lands" level of exact !!

    This guys video demonstrated perfectly the Variance in measurements, so I guess I am OK, at least for the UK right

    So, am I pushing my bullet in too hard ??

    Good Question LJ, I was gonna say, "Yeah If you can get the measurements all the same..."
    Bet you can't wait to start all the measuring, how many rifles are you gonna be loading for now? It really is fun tho, not frustrating but challenging in my opinion
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    Variance between measurements is why I like to compute the average of five measurements. When I've stuck the bullet into the lands (which I am pretty good at doing now and then), I've always concluded that I was pushing too hard and I disregard that measurement when computing the average.

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    If I understand the question correctly; you are asking if once you have a distance from the base of the brass to the land diameter of the bullet using a comparator that just touches the lands, will this be the same measured with the comparator for a different bullet.

    The answer, depends on the throat angle, and bullet shape. There are many different ways the bullet can contact the lands depending on the relative shape of the bullet and the angle of the throat. The idea is that land diameter (where most comparators measure) may or may not have any relation to contact diameter. Ideally you would have a comparator that had the same throat angle as your rifle. If you have a rifle rebarreled it is not much work to cut a comparator with the throat/or chamber reamer, which would be a good investment.

    I have a little sketch I just made that hopefully will make some sense. It shows a 2 degree throat which is a reasonable value for modern cartridges but many older rifles have throats of 5 degrees or so. I will post up the sketch tomorrow when I can scan it at work, my digital pictures are unreadable.

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    Supporting Member iofthetaiga's Avatar
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    Quote Originally Posted by kodiakrain View Post
    So, am I pushing my bullet in too hard ??
    Uh-huh.

    Edit: OK, in all fairness, I stick the bullet 50% of the time, no matter how delicate I am. Usually I can knock it loose tho by simply thumping the action once or twice against my palm, so it's not really stuck hard. The average of a few measurements with the Hornady tool should have you as accurate as you're going to get. By my experience it's much more accurate than the old smoking method, no matter how careful you are with that.
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    One small piece of the puzzle that needs to be considered if your really getting ready to split hairs.

    If you have the other pieces to the Stoney Point system that allow you to measure the mid point of the shoulder to the head of the case you will need to compare the difference between the modified case and your fired brass. With my 338 Lapua I used my fired brass and made the modified case from that.

    With my 308 I bought a modified case from Hornady and it is .007 shorter than my fired brass. Once the measurement is made with the purchased modified case I add the difference to that measurement to get the real distance.

    The error is because the shoulder determines the head space with non belted cases and that makes the COAL shorter by the distance since you are pushing the case in until it stops.

    Cheers,

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    Supporting Member iofthetaiga's Avatar
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    Quote Originally Posted by marshall View Post
    One small piece of the puzzle that needs to be considered if your really getting ready to split hairs.

    If you have the other pieces to the Stoney Point system that allow you to measure the mid point of the shoulder to the head of the case you will need to compare the difference between the modified case and your fired brass. With my 338 Lapua I used my fired brass and made the modified case from that.

    With my 308 I bought a modified case from Hornady and it is .007 shorter than my fired brass. Once the measurement is made with the purchased modified case I add the difference to that measurement to get the real distance.

    The error is because the shoulder determines the head space with non belted cases and that makes the COAL shorter by the distance since you are pushing the case in until it stops.


    Cheers,
    Just to be clear here, you're saying that the modified case is shorter from the shoulder to the case head, correct? You're NOT referring to the over all case length measurement...
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    Quote Originally Posted by LuJon View Post
    OK, I have been watching vids and reading up on this and it seems that everyone does things their own way.... It seems that one could use one of the various COAL gauges either home made or commercial and get the COAL using ANY bullet. Once they have that done then using a bullet comparator gauge like the one from Sinclaires to find the Ogive you should be able to find the cartridge length to the Ogive for your rifle.

    Once you know the COAL measured to the Ogive for your rifle it seems like there would be no need to test each different bullet in the rifle with the COAL gauge. Can't you just load any new bullet to the same COAL measured to the Ogive?
    Without even reading the answers you will get from others on this thread, let me say that you are absolutely RIGHT.

    The distance to the lands, doesn't change. You can establish that distance in several different ways, and even with ANY bullet.

    That Sinclair (NUT) lookin Comparator is the greatest one IMO. The hole for the caliber you're using can be used to set the OAL to the lands, (Once you've established it.) for any bullet you choose.

    Then, you adjust the seating stem in your seating die, to that.

    That's the way I do it. I know the distance to the lands for a particular rifle, and I use the Comparator/NUT to set the bullet off the lands by .030, usually.

    Sure, the OAL to the TIP, changes, and your seating adjustment, but the distance to where the bullet contacts the lands, DOESN'T CHANGE.

    (The instructions for the Stony Point Tool, from H___L, now Hornady, will mislead you into thinking you need to establish a length for each bullet.) Whoever authored that bit of advertising hype, is full of Bee's Wax.

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    Quote Originally Posted by Doc View Post
    Variance between measurements is why I like to compute the average of five measurements. When I've stuck the bullet into the lands (which I am pretty good at doing now and then), I've always concluded that I was pushing too hard and I disregard that measurement when computing the average.
    Hi Doc:

    So then, you are getting an AVERAGE distance. ????

    You will get variances with any method you use, but some are better than others, and one method may better suit your ability to accomplish it accurately.

    IME, the Stoney Point/Hornady Tool is the Most Problematic of all. The problem of getting an accurate distance in the first place is exasserbated by the near impossibility of obtaining an accurate measurement of that distance, with everything strung out and wobbling on ya whilst you try to hold it all straight inside your Caliper.

    I prefer the methods in which you use an actual case and a bullet, but I also use the wooden dowel method, sometimes.

    If your goal is to seat .030 off the lands, you have margin for error. It is those who claim that they are .001 to .002 off the lands, who are fooling themselves and many others.

    Perhaps, itís more important to have all your bullets seated the SAME distance from the lands, than to know that distance to the last .001 ?? I think so.

    Smitty of the North
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    Quote Originally Posted by iofthetaiga View Post
    Just to be clear here, you're saying that the modified case is shorter from the shoulder to the case head, correct? You're NOT referring to the over all case length measurement...
    In my example yes. Using the modified case and determining an Ogive distance that total number is .007 shorter than if I would use fired brass. It's that way because the fired brass is .007 longer between the mid point on the shoulder and the head in my 308. Since the modified case is pushed in against the chamber and the bullet is pushed in against the lands that measurement will be off by the difference between the head and shoulder on the modified versus your fired brass.

    I have several modified cases to measure for different rifles and they all vary due to chamber specs. When I had the 338 Lapua built I made the modified case from brass fired in that chamber to alleviate any discrepancy. All you need to do is drill and tap the head and ream the neck. Hornady will do it for you if you send in your fired brass.

    I enjoy Smitty's responses but I don't have any issues getting precise measurements from the Stoney Point System. Perhaps it's my machine shop back ground that allows me to get consistent measurements. No disrespect intended but a wooden dowel and a pencil or flame smoke and a scribe can't be as accurate as a caliper and a fixed solid metal tool.

    I also like the nut that Smitty makes reference to but it has the same chance of error as any other tool not properly used.

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    I have done it the trial and error method with actual seated bullets until it is just off the lands my whole reloading life. I only do this once with any given bullet because I have a dumby round in every set of dies for setting seating depth the next time.

    I'm probably the odd duck on this thread because each rifle I have has one purpose(coyote gun vs deer gun etc) and once I get figured out what combo works the best in that rifle to achieve that purpose I never vary from it.

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    Quote Originally Posted by Smitty of the North View Post
    Hi Doc:

    So then, you are getting an AVERAGE distance. ????

    You will get variances with any method you use, but some are better than others, and one method may better suit your ability to accomplish it accurately.

    IME, the Stoney Point/Hornady Tool is the Most Problematic of all. The problem of getting an accurate distance in the first place is exasserbated by the near impossibility of obtaining an accurate measurement of that distance, with everything strung out and wobbling on ya whilst you try to hold it all straight inside your Caliper.

    I prefer the methods in which you use an actual case and a bullet, but I also use the wooden dowel method, sometimes.

    If your goal is to seat .030 off the lands, you have margin for error. It is those who claim that they are .001 to .002 off the lands, who are fooling themselves and many others.

    Perhaps, itís more important to have all your bullets seated the SAME distance from the lands, than to know that distance to the last .001 ?? I think so.

    Smitty of the North
    Hey Smitty,

    You're a character, and I've appreciated your membership here over the years...you know what I'm saying. No matter what method you use there will be variance, which you said yourself. Taking the measurement five times then averaging gives you a better chance of being closer to the actual distance to the lands for that rifle/bullet combination. I like and agree with your point about people fooling themselves if they think they are exactly off the lands to a .001 or .002 margin. I think your words are very true. Your point about ensuring that all the completed rounds have the same distance from the lands is true and an obvious part of consistency when handloading, but you need to know where to start in the first place, which led to your really comical description of using a Stonypoint gauge...it was funny. I will agree that it has taken practice to be able to use that thing without feeling all thumbs with it. However, once you get there, it really does work very nicely.

    Now, back to the original question...it sounds like we are all generally agreeing in theory (and some in practice) that once the approximate distance to the lands for a particular rifle/bullet combination is determined (using the method of your choice), you can then use a bullet comparator to determine the seating depths for other bullets in that rifle without actually measuring those other bullets in that rifle. Can I see a show of hands?

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    See the attached. The 2 lines on the right side are the land and grove diameters, at the typical 0.004" grove depth and a 2 degree throat this gives a tapered portion of the throat 0.115" long. As you can see in the sketches land contact may occur any where in this .115" length depending on the shape of the bullet. Hopefully the sketch is understandable.
    Attached Files Attached Files

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    Default Nothing personal, of course. Just wanna be clear on this.

    Quote Originally Posted by marshall View Post
    I don't have any issues getting precise measurements from the Stoney Point System. Perhaps it's my machine shop back ground that allows me to get consistent measurements. No disrespect intended but a wooden dowel and a pencil or flame smoke and a scribe can't be as accurate as a caliper and a fixed solid metal tool.

    I also like the nut that Smitty makes reference to but it has the same chance of error as any other tool not properly used.
    A "machine shop background" would certainly be an advantage, when using any measuring tools.

    I tried Fire Formed Modified Cases, too, and although they were closer to the shoulder length of my rifle chamber than the standard ones you buy, they were looser in the neck, introducing some more wobble, when it was time to measure.

    With that Stinky Point Tool, after you THINK you have an accurate distance, you gotta measure it. It's a little hard to explain verbally.

    One jaw of your caliper is in a step of the tool, and against the case head, with that rod of the tool hanging out there. Then there is the bullet wobbling around inside the case neck, contacted by the comparator, maybe another 2 inches in length, which is set screwed onto the other jaw of the caliper. Hope, you have it in exactly the right place.

    Well, "fine and dandy", but you have quite a distance there, and you gotta keep it ALL STRAIGHT in between, and CENTERED on the ends, so you can measure it accurately. That's where the rub comes in. Keeping it all aligned, and getting the same measurement each time.

    For me, it wasn't happenin. Naturally, I am dubious that this tool works well, for anyone else either, given the possibilities/probabilities for error.

    I had ALL the Stinky Point Tools, and I packed'em up and gave'em away. Watta RELIEF. If I had more character, I'd have THROWN them away.

    Sinclair makes their own Tool for the same purpose, that is entirely different. They say it's harder to use than the Stinky Point Tool but more accurate. IMO, it is. Much more accurate/consistent readings.

    RCBS has their Precision Mic.

    I consider BOTH of these tools, and any other method, and there are many, I've tried to be far superior to the Stinky Point. Although it's principal is sound, I find it is limited by it's design, that almost insures inaccuracy.

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    Smitty you're hilarious, is it natural or do you work hard at it?

    I don't have any of the wobbly issues you are talking about.

    I don't have a picture of the modified case attached to the tool but the caliper measures both the same way as seen in this picture. I put the red fixture with the caliber specific bit on the blade loosely then close the caliper and tighten the fixture. After that I zero the caliper and measure, nothing to it

    On another note, I've seen guys that can't even measure the thickness of a feeler gauge with a caliper. They get a different number each time, go figure...

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    Hmmm.... I don't think the tool is the problem here.

    Hey Smitty, have you tried adjusting the nut attached to the close end of the tool?

    Joking aside, I get greater precision from my Hornady gauge than I can set my actual COAL to. Of course, I'm working with a Lee Loader at this point...
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