Thread: COAL ?
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Old November 2, 2012, 05:31 PM   #6
Join Date: March 4, 2005
Location: Ohio
Posts: 14,989
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.


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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