COAL, OAL, Length to ogive? Please help me unconfuse the differences.

Many posts about bullet "jump" to the lands mention changing COAL OR OAL to increase or decrease this "jump" a precise number of thousandths of an inch. I am of the impression that COAL AND OAL refer to the overall length of the cartridge from base of the brass to the tip of the bullet. Because all bullets, even the best in the same batch, have slightly different (.001" to .005") ogive lengths, how can one accurately judge the precise length of "jump" just by seating the bullet deeper or shallower into the case. Seating the bullet deeper will certainly increase this "jump" and seating the bullet shallower will certainly decrease this "jump". However, the overall length of the cartridge does not determine the "jump" to the lands. The length of the cartridge from the base to the ogive of the bullet is what determines the amount of "jump". One needs a special procedure and gauge to measure this distance.

Please feel free to correct any misunderstanding I have about the calculation of bullet "jump" and the abbreviations describing the length of the cartridge from the base of the case to the ogive of the seated bullet.

How is this measurement-base to ogive length-described in reloding terms- OAL to ogive, OALTO, etc. ?

Thanks in advance.

Your spot on. I refer to OAL as being from the cartridge base to ogive. I measure all my bullets and segregate them as to length from bullet base to ogive. For benchrest, I get a bit more anal and measure by weight too.

You aren't confused at all ;) I think over the years OAL was expressed in R/L manuals as a tip to base measure. Then some folks began expressing it as COAL for Cartridge Over All Length. Then people realized the only really accurate measure was ogive to base and cartridge OAL became COMPARATOR oal ??? I agree w/ you. We need a new standard like O to B or OTB to express this more accurate measurement.

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Originally Posted by John_M

Many posts about bullet "jump" to the lands mention changing COAL OR OAL to increase or decrease this "jump" a precise number of thousandths of an inch. I am of the impression that COAL AND OAL refer to the overall length of the cartridge from base of the brass to the tip of the bullet. Because all bullets, even the best in the same batch, have slightly different (.001" to .005") ogive lengths, how can one accurately judge the precise length of "jump" just by seating the bullet deeper or shallower into the case. Seating the bullet deeper will certainly increase this "jump" and seating the bullet shallower will certainly decrease this "jump". However, the overall length of the cartridge does not determine the "jump" to the lands. The length of the cartridge from the base to the ogive of the bullet is what determines the amount of "jump". One needs a special procedure and gauge to measure this distance.

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Correct, the Cartridge Overall Length(COAL) or abreviated, Overall length(OAL) is the base of the brass to the tip of the bullet.
The issue as you have mentioned, is that Ogive's vary, as well as the Barrels. That is why you don't see a procedure for a specific length listed anywhere. COAL determines the "jump", but ONLY in a SPECIFIC barrel, with SPECIFIC components.
MZ5 and I had matching 10FP's in 223. Using the same brass and bullets the throats were different. So what I used, he could not. The COAL's, or OAL's listed are(should be anyway) SAAMI spec's that ARE safe in any gun. Specific jump lengths are on an individual basis only.

The main reason for this oal is to make sure your bullets will fit the magazine or clip if you will..

There is a special tool to get the correct ogive lenght.You have to pardon my spelling..I got one
from Sinclair reloading company..It is called a ogive comparative tool..It measures just to the
ogive of the bullet.Works with any bullets of the same diameter..So if your shooting a .308 bullet
thats the one you need,for 30 cal....223 diameter,etc....And your right about trying to measure to the bullet tip.
It is never the same..Good luck with it....John

Thank you gentlemen, all. You have the explained the measurements and abbreviations as I thought they should be used. You have successfully unconfused me. ;D

I have been using the Hornady Lock-N-Load OAL Gauge and their Bullet Comparator with a very accurate digital caliper to successfully seat bullets to different "jump" distances. These not-too-expensive tools are easy to use, accurate, and invaluable if one is to achieve PRECISE bullet "jump" distances. Similar high quality measuring gauges are made by other manufacturers of reloading equipment.

As gotcha suggested, it would be helpful if a proper organization (SAAMI?) would make an effort to define the various cartridge measurements and their abbreviations. This would allow us all to understand precisely what others are saying and asking. ;)

Best wishes, John_M