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Old June 23, 2012, 07:19 PM   #1
DeerSlayer86
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COAL question

Is it better to measure the length from the ogive or tip to tip? And why? Thanks guys
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Old June 23, 2012, 07:43 PM   #2
PA-Joe
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If you look a the tips you will see a lot of variation from one bullet to the other. Particularly with lead tips.
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Old June 23, 2012, 07:56 PM   #3
wncchester
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Measuring COAL/OAL means from the head to the meplat.

But no firearm cares where a bullet nose hangs in the air, all that matters is the bullet's jump to the rifleing. And that requires knowing where the lands are and measuring seating to the point of rifleing contact on the ogive.
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Old June 24, 2012, 09:03 AM   #4
hooligan1
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From the case Head, to the Ojive of the Bullet.
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Old June 24, 2012, 09:31 PM   #5
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Not sure as to the point of your question, but I'll make a point in case you aren't aware...elaborating on what wncchester said...

When precision loading for bolt actions, the distance from the ogive of the bullet to where it touches the rifling is important. This will vary with EVERY bullet, even those of identical weight but different ogives.

The best way to load these bullets is with an OAL gauge, and a bullet comparator. You then measure the comparator length at which each bullet touches the rifling- and experiment with the "jump" Usually, around .02 is the magic number.

This matters little with semi's, as you're limited to mag length and they have generous chambers anyway.
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Old June 25, 2012, 11:39 PM   #6
judgecrater
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Just keep in mind when reading a load in a manual you use total length.
This is quite different than considering bullet jump to the rifling for best accuracy in a rifle.
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Old June 26, 2012, 08:52 AM   #7
CS86
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Below are a couple references on COAL, and bullet jump. I was going to write something up on COAL and bullet jump, but I think tobnpr covered what I was going to say.

http://thefiringline.com/forums/showthread.php?t=483258

http://www.shootersforum.com/handloa...d-bullets.html

As for your question. You can measure from either the Ogive or tip. If you can measure from the Ogive it would be better I think, but anything with a hard tip, such as a balistic tip, should be pretty close for accuracy. Soft points aren't the best from measuring from the tip. You will end up with different COALs, from the tips, at each bullet seating. Soft points just don't stay as uniform. If you want to fine tune a little more you would get a bullet comparitor. Again this is pretty much what tobnpr said.
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Old June 26, 2012, 02:22 PM   #8
FiveInADime
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I don't have any of the gauges to measure the distance to the lands, but there is a way to work around that and find a good seating depth for accuracy. Before I started reloading my .243 for the first time, I made a shell with a once-fired piece of brass from my gun and a Lee Collet neck-Sizer that had just enough neck tension to hold the bullet. I glued a Dowell into the empty primer pocket.

I then seat a bullet with my fingers far enough out to guarantee that it will touch the lands. I take the bolt out of my rifle and push the dummy-shell into the chamber with the Dowell, slowly and carefully until the shoulder seats in the chamber. Then I, carefully, pull it out and measure to the tip of the bullet several times. The measurements should be within a couple thousandths. Average the measurements to get a working number.

It's not a perfect measurement, but it let's you know where a particular bullet hits the lands +- a couple thousandths. I started .02 off the lands for my first loads and I indexed that depth on the seating die with a marker. If I want to adjust them deeper for that same bullet I just seat to the indexed depth, measure, and then turn the stem a little at a time until I get to my new seating depth. For each new bullet I use in the .243 I use a different color Sharpie to index the seating depth, but I found that the 70gr Nosler BT and the 87gr V-Max seat to almost exactly the same depth so I use one mark for those two.

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Old June 26, 2012, 07:08 PM   #9
mrawesome22
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^^^^ Do a forum search for "hacksaw".

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Old June 26, 2012, 07:48 PM   #10
FiveInADime
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Quote:
Originally Posted by mrawesome22 View Post
^^^^ Do a forum search for "hacksaw".

Sent from HenseMod6.
I know what you're referring to and that is the way to go if you do not have a Lee Collet neck-Sizer. I like the control you have on the tension with the neck-Sizer. Either way the procedure is the same.


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Old June 27, 2012, 07:48 PM   #11
zeke
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COL (COAL) (OAL) is measured from base to tip, plain english.

Some rounds need COL measured to ensure function in a particular firearm. Too long and the round may not function in the action, or fit in the magazine. Maximum COL is usually listed in most reloading manuals, and firearms manufacturers pay attention to it.

Another good measurement is for headspace to use on a loaded round. Perhaps measured from base to forward portion of bullet that contacts the rifleing. Then you may be able to use this mesurment when setting up die or perhaps trying another bullet.
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Old June 27, 2012, 08:14 PM   #12
Lost Sheep
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Three things

Quote:
Originally Posted by wncchester
Measuring COAL/OAL means from the head to the meplat.

But no firearm cares where a bullet nose hangs in the air, all that matters is the bullet's jump to the rifleing. And that requires knowing where the lands are and measuring seating to the point of rifleing contact on the ogive.
COAL/OAL is supposed to be measured from the tip of the bullet (or meplate in the case of a flat-nosed slug) to the base of the brass.

However, every firearm does care about more than the bullet's jump to the rifling. (which is important for accuracy)

In addition to that jump (freebore), a cartridge needs to be of a length to feed through the action of the firearm. Not too long to fit in the magazine, not to short to feed up the feed ramp. (important for reliability of function)

But, even more important for safety, the space under the bullet is vital VITAL VITAL. But you can't measure it directly, so every recipe for a particular bullet weight and shape depends on the assumption that all those bullets are the same length from tip to base. Subtract that distance and the thickness of the web from the OAL and you find the free linear space where the powder is. Reduce that space and you get a rise in pressure. So, if you have a spire point bullet of 100 grains loaded to the same OAL as a flat point bullet of 100 grains (assuming the materials composition of the bullets are the same) you will have less space under the spire point and experience higher pressure. Depending on the cartridge, maybe LOTS higher.

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