COL vs OAL

[dmy]

I'm new to this forum and suspect it is probably posted somewhere. However, can someone explain the difference between COL vs OAL when it comes to proper bullet seating? Thanks.

[BigBronco]

Two different acronyms for the same measurement.

http://www.calguns.net/calgunforum/showthread.php?t=402624

For Rifle it is best not to rely on COL or OAL and seat based on ogive.

[noylj]

COL is Cartridge Overall Length (see how nice and descriptive COL is?) and has always been the preferred term
OAL is Overall Length and can be applied to ANY object you can measure. The case has an OAL. The bullet has an OAL. The gun has an OAL. However, ONLY the cartridge has a COL. However, in most cases COL = COAL = OAL = Cartridge OAL. I have even seen OACL and OALC.
In almost all cases, the drawing should specify the distance from case head to a datum point where the bullet reaches a certain diameter.
There are a lot of terms that are misused, even by the industry.
Most folks have no idea what a clip is and think that it is the "hip" term for a magazine.
Most folks say they are shooting a 9mm, and we are left to "assume" they mean 9x19/9mm Luger/9mm Parabellum, rather than a dozen or more other 9mm pistol cartridges. Some even write that they are shooting a .9mm (which would be a .0355" diameter bullet).
I would say to look in a manual, but the folks that write them seem to often NOT be that knowledgeable about correct terminology (just like many folks in various industries, they pick up "slang" terms).
You will hear folks talk about reloading a bullet. What they mean is a reloaded cartridge. The bullet is the projectile that leaves the muzzle and does not include the case/primer. Some are so convinced that they load bullets, that they call the bullet a "bullet head" or just "head."
It is to the point where so many no-gun folks hear the cartridge and the bullet referred to as the bullet, that they draw the whole cartridge coming out the barrel or being in the person's body (when Reagan was shot, at least one newspaper (I think NYTimes) showed a complete .22LR cartridge next to his heart).

[Meety Peety]

To be fair, when measuring a cartridge for seating depth, there is really only one "overall" length - the cartridge. If someone asked you how long a pencil was would you tell them the length of the pencil stick, plus the tip, plus the eraser? No because all of the components assembled create an object, and that object now has one total overall length.

As Bronco stated, the only variation worth concerning yourself with is measuring from the tip or the ogive.

[noylj]

MeetyPeety:
Really? I don't mind someone asking about the cartridge OAL. Since everything has an OAL, then you have to put a modifier before OAL to establish what you're asking about.
The thing is, the question is "I have xxx bullet—what OAL should I use?"
There is NO reference to cartridge other than we ASSUME that is what the poster is asking about. CLARITY is good. Using the correct term is NEVER a bad thing.
Face it, the OP posted because the use of OAL was NOT clear to that person. However, COL is clear as to being about the complete cartridge.

[dmy]

Thanks all.

Thank you all. I now understand the difference between COL and OAL or OACL or OALC, or in some cases, the lack of a difference.

[silas3d]

Good discussion. I had the same question back when I started reloading. Since then as I work up new loads that aren't directly in manuals (e.g s&w 500 magnum using a plated 335gr hollow point) I realized that what is more important is the volume within the cartridge when the bullet is seated because this volume directly affects the pressure when fired. More volume = less pressure. As a practical point I make sure to NEVER reduce the case volume below what I calculate from the published COL. I often seat revolver rounds to a longer COL than published, but never to a shorter one.

Safety is mandatory. Follow your manual.

Hope that made sense...