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Old October 30, 2012, 02:48 PM   #1
rebs
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COAL ?

Loading for my Ar.
I am loading lake city 223 brass with a cci 400 primer, 24.9 of H335 powder, 55 grain Hornady spire soft point bullet and a coal of 2.255, the accuracy is excellent 1/2 " groups at 100 yards.
The Hornady book says coal for that bullet is 2.200, I tried that and the accuracy dropped way off, why ?

If I loaded a coal of 2.200 would I be able to match the accuracy by using less powder ? By seating the bullet deeper in the case to get the coal of 2.200 that would leave less space inside the case so would less powder give me the same pressure and velocity and accuracy ?
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Old October 30, 2012, 02:53 PM   #2
Brian Pfleuger
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Quote:
The Hornady book says coal for that bullet is 2.200, I tried that and the accuracy dropped way off, why ?
Cuz Hornady didn't develop their data with your gun.

Quote:
If I loaded a coal of 2.200 would I be able to match the accuracy by using less powder ?
Maybe. Or possibly with more powder.... only one way to know.

Quote:
By seating the bullet deeper in the case to get the coal of 2.200 that would leave less space inside the case so would less powder give me the same pressure and velocity and accuracy ?
Actually, until you REALLY start to intrude on powder space, making a rifle round shorter tends to DECREASE pressure, because the "running start" into the rifling more than compensates for the decreased space. Longer rounds give less running start and require more pressure to engrave the bullet.

UncleNick has a chart he posts from time to time which shows the affect of OAL changes in .308 (I think it's .308). I don't have a link to it but maybe he'll be around to show it and expound on it...
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Old October 30, 2012, 07:21 PM   #3
theshephard
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Distance to lands??

One thing is for certain - by decreasing your COAL, your increasing the 'jump' or distance between the bullet ogive and the lands of the barrel's rifling.

It's a pretty common belief that by dialing in the OAL (not COAL) to minimize jump, you'll see better accuracy. This may explain why, as you seat the bullet farther out of the case, you're seeing better or at least more consistent accuracy.

Hornady themselves even make a tool to help you with this, called the Lock n Load OAL Gauge.
You can read more about this here:
http://www.6mmbr.com/catalog/item/1433308/977259.htm

For the record, some people dispute this as superstition so YMMV, but as the prior poster alluded - you can only find out by experimenting, keeping records, and evaluating the data yourself.
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Old November 2, 2012, 03:41 PM   #4
tobnpr
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OAL in the "books" is just a guide...
Military rifles and semi's like the AR typically have more generous chambers to help ensure functionality. Tighter tolerances may mean more accuracy, but also a higher possibility of malfunction in a production weapon system.

Keep at least one bullet dia. in the case neck, and experiment with the bullet comparator as suggested above- and you'll need the OAL gauge and a .223 modified case to go with it.

As long as you've got enough bullet in the case neck for adequate tension, and you're not jamming the ogive into the rifling, you're gtg...
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Old November 2, 2012, 03:55 PM   #5
wncchester
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"Keep at least one bullet dia. in the case neck, "

Why is that? I mean a lot of cases don't have necks one bullet diameter long. And a lot of people load without concern over how much bullet is in the neck so long as it doesn't fall out with normal handling. ??
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Old November 2, 2012, 05:31 PM   #6
Unclenick
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Yes. The 1 caliber into the neck thing was an old rule of thumb. The fact .308 Winchester and .223 Remington necks are less than a caliber long is why you can find published opinions from the 50's and early 60's that the necks of those two rounds are too short to ever possibly allow them to match the accuracy of the .30-06 and .222 Remington.

The actual relationship between seating depth and accuracy is complicated. The chart Brian referred to actually was .30-06 round nose bullet data from the Lloyd Brownell study of absolute pressure published in 1965. It shows pressure of a fixed powder charge having a minimum value seating depth, and being higher either side of that seating depth. Brownell felt it was a point where dominance of the fact seating deeper reduces the powder burning space increases pressure and fact a longer seated bullet doesn't allow as much gas to bypass the bullet before the bullet obturates the bore was the real explanation.

But here's where it gets complicated. There seems to be at least one and sometimes two or, rarely, even three different seating depths at which a particular bullet is most accurate in a rifle. Berger has a procedure for finding the best depth here. It's as if there is some location where the bullet jump and the gas stream around the bullet work to best center it in the bore. The problem is that when you tune seating depth you are changing the pressure, velocity, and barrel time simultaneously if you don't also retune the load. That can be done with the assistance of QuickLOAD to neutralize it, but getting those two varables isolated has tripped up many a handloader.




Theshepard,

The terminology has changed over time. The old Rifleman magazines commonly spoke of Cartridge Over-All Length, or Cartridge OAL, which many abbreviate as COAL even today. Some would drop the "Cartridge", as you do, to get OAL. But strictly speaking, neither is current. The problems is that sometime between about WWII and the 1960's the usage of "overall and over-all" changed.

In my Webster's 2nd edition (1948 printing), the word overall, a compound word that dates back to Chaucer, meant only to take altogether, as in, his life was good overall. The hyphenated form was used exclusively to describe physical length as in, the boat was 22 feet over-all. Obviously the initial for "Overall" would just be "O", while "Over-All: has two initials, "OA".

By the time you get to Webster's 3rd unabridged (mine was printed in 1966), the hyphenated form is completely gone and length is also being written as the compound word with the single letter initial. Thus Cartridge Overall Length is the modern term, or COL. OL is all you use if you want to drop "cartridge" from the description, though that can lead to confusion if the context isn't clear, as overall lengths of guns are also a topic of discussion at times.

The time to correct people is when they use AOL, having confused cartridge length with the once-popular online service.
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Old November 2, 2012, 08:10 PM   #7
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Awesome!!

Unclenick, if I could 'LIKE' your post, I would do so! Great information and I truly appreciate the level of detail. I tried to post a helpful tip, and got an even more helpful one (for me) in return. That's community, man!
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