The Firing Line Forums

Go Back   The Firing Line Forums > The Skunkworks > Handloading, Reloading, and Bullet Casting

Reply
 
Thread Tools
Old March 31, 2013, 10:12 AM   #1
Nathan
Senior Member
 
Join Date: July 1, 2001
Posts: 1,941
Reloading Measurement Definitions

I have seen some posts here, even my own where these terms are getting messed up, or I'm me saying them up, so I want to define them here and have you correct me or define your own.

To me, measuring OAL is:

Main purpose is magazine fit.

Measuring COAL(Comparator OverAll Length) is:

Or

Measured to assure proper fit between load and barrel. Generally expressed as [Lands] -#.###

COAL(gun) is measured:




Headspace(cartridge side):

Best expressed as fired +/- #.### as every gun will be different.
Nathan is offline  
Old March 31, 2013, 10:13 AM   #2
Nathan
Senior Member
 
Join Date: July 1, 2001
Posts: 1,941
Neck Run Out(RO):

Measured middle of the neck.

Bullet Run Out(RO):

Measured about where the bullet is full caliber diameter.

Case Length:

Longest measurement recorded. Should be measured after sizing.
Nathan is offline  
Old March 31, 2013, 10:24 AM   #3
243winxb
Senior Member
 
Join Date: July 26, 2011
Posts: 974
SAAMI Glossary - Definition of terms

SAAMI Glossary http://www.saami.org/glossary/display.cfm?letter=A Results
243winxb is offline  
Old March 31, 2013, 11:49 AM   #4
F. Guffey
Senior Member
 
Join Date: July 18, 2008
Posts: 2,641
Quote:


COAL(gun) is measured:
________________________________________________________________
Overall is one word, run overall through spell check. Then it becoms OAL, after getting used to using OAL, decide if there should be the word ‘maximum’ added to the term OAL as in maximum OAL, or minimum OAL.

One of the most boring conversation I can get involved with starts when someone says or starts the conversation with, “Repeat after me.....”. Then there is “SAAMI says....”. SAAMI does not list head space on the cartridge, SAAMI list head space of the chamber, the case length is listed from the mouth of the case to the head of the case and from the shoulder/datum back to the head of the case, the case has ‘CASE LENGTH’, but the ‘repeat after me’ claims the case has head space.

Then there is the difference between ‘head space’ and case length when measured from all the usual places, there has to be a plus side and minimum (-) side. In the perfect world when COL is measured the difference between the two measurements (lengths) is not included, MEANING! the measurement is not absolute because the bolt in laying on the bench beneath the rifle as illustrated by the picture. Then there would be the suggestion ‘measure the length of the chamber first’ most fire to form, then there are the few that form first then fire.

F. Guffey
F. Guffey is offline  
Old March 31, 2013, 03:11 PM   #5
Nathan
Senior Member
 
Join Date: July 1, 2001
Posts: 1,941
Guffey,

I'm totally confused by your post, sorry.

One thing I think I see you getting hung up on is SAAMI. They are pretty important, but their real purpose is so all 308 Win ammo fits and works in all 308 chambers. So, the set a nominal which gun makers work above and ammo makers work below. Pressure and dimensions. This has little to do with handloading as handloaders make ammo for their guns only. Still, it is a good guide to fit and safety.

Also, I think SAAMI defines headspace as a bolt face to shoulder datum measurement. In my notes, I call them headspace(fired) and headspace (load) as the corresponding lengths on my cases. To rename them loses too much meaning to me. If I had a chamber cast that I measured, that would be headspace (gun).

My real driver with this thread was the OAL issue. I see too many people measuring OAL as defined above as an important ballistic measurement, but a quick look through my bullets tells me that the point is excess material(and varies +/- 0.005" even on good bullets!) and that the ogive is the point to measure....actually, where the ogive and the bearing surface meet to be precise...I.e. the Hornady gages.
Nathan is offline  
Old March 31, 2013, 04:19 PM   #6
ScottRiqui
Senior Member
 
Join Date: January 27, 2010
Location: Norfolk, VA
Posts: 2,905
Quote:
My real driver with this thread was the OAL issue. I see too many people measuring OAL as defined above as an important ballistic measurement, but a quick look through my bullets tells me that the point is excess material(and varies +/- 0.005" even on good bullets!) and that the ogive is the point to measure....actually, where the ogive and the bearing surface meet to be precise...I.e. the Hornady gages.
I understand your frustration, but you'll have to come up with your own term for comparator measurements to the ogive; the 'C' in COAL stands for "cartridge", not "comparator". Both OAL and COAL refer to the same thing, the distance from the base of the cartridge to the tip of the bullet. That's not always the most repeatable measurement, or the most useful, but it's better than trying to redefine terms that have been in use for decades.
ScottRiqui is offline  
Old March 31, 2013, 04:21 PM   #7
g.willikers
Senior Member
 
Join Date: September 28, 2008
Posts: 5,139
Thanks for the clarification through pictures, Nathan.
Nice job.
__________________
Lock the doors, they're coming in the windows.
g.willikers is offline  
Old March 31, 2013, 04:26 PM   #8
hooligan1
Senior Member
 
Join Date: July 18, 2010
Location: Independence Missouri
Posts: 3,296
Don't be confused, he's a genius and they make theirselves happy by making all us not genius people feel dumber...
Coal is Cartridge Overall Length, Oal, is what is measured by the Comparator. That's my interpretation.
__________________
Thanks for coming!
hooligan1 is offline  
Old March 31, 2013, 06:09 PM   #9
trobin
Senior Member
 
Join Date: February 26, 2013
Location: Louisiana
Posts: 115
Hooligan1.... Agreed
trobin is offline  
Old March 31, 2013, 06:22 PM   #10
William T. Watts
Senior Member
 
Join Date: January 20, 2010
Location: Central Arkansas
Posts: 765
This how I determine my OAL for for every rifle I own!

I use a 1st fired case from my rifle and drop it in a L.E.Wilson cartridge case gage, mic from case head to max step on the case gage using a depth mic to determine how much the case has lengthen on firing. Once I have determined how much the case has lengthened I adjust my sizing die to that measurement plus .001" (your reducing the case length by .001). Pretty simple, I use a sized case and start a bullet in the neck of the case then insert into my chamber using my fingers to push the case until bullet touches the rifling in the barrel. While holding the case/bullet in place I push a cleaning rod down the muzzle of the barrel until it touches the bullet tip, pull the cleaning rod out a 1/4" place tape around the cleaning rod push the rod in until bullet tip touches again, mark the tape with a pen. I usually start at this measurement less .010" when developing a load for a rifle and adjust for best accuracy. I try to keep things as simple as I can, there are variations of this method, it does work and I use tools I already have.. William

Last edited by William T. Watts; March 31, 2013 at 06:30 PM.
William T. Watts is offline  
Old March 31, 2013, 06:23 PM   #11
NWPilgrim
Senior Member
 
Join Date: September 29, 2008
Location: Oregon
Posts: 2,149
I see manuals listing COL (cartridge overall length) and OAL (OverAll Length) but I have never seen COAL except on the interwebz. It is irrelevant though as all three stand for the same thing and it is nitpicky to worry about which is used. I can also understand "creek", "crick" and "stream".

COL is IMPORTANT for ballistics (internal) when referenced for a particular bullet and powder charge. When a manual specifies a COL for its load data, that means a certain amount of case capacity is taken up by the bullet when seated to that COL, and this will affect peak pressure. If you load to a significantly shorter COL then you are likely to get higher pressures than indicated in the load data, especially in the smaller cases of handgun cartridges.

So, yes, when loading cartridges it is important to know the referenced COL for the bullet and powder you are using and the effects of using a different bullet or COL.
__________________
"The ultimate authority ... resides in the people alone. ... The advantage of being armed, which the Americans possess over the people of almost every other nation ... forms a barrier against the enterprises of ambition."
- James Madison
NWPilgrim is offline  
Old March 31, 2013, 06:26 PM   #12
ScottRiqui
Senior Member
 
Join Date: January 27, 2010
Location: Norfolk, VA
Posts: 2,905
Quote:
Oal, is what is measured by the Comparator
Quote:
Hooligan1.... Agreed
That doesn't make sense - what exactly is "overall" about a measurement taken from the base of the cartridge to a point on the ogive?
ScottRiqui is offline  
Old March 31, 2013, 06:39 PM   #13
trobin
Senior Member
 
Join Date: February 26, 2013
Location: Louisiana
Posts: 115
So what do you use to refer to the measurement from base to ogive?
trobin is offline  
Old March 31, 2013, 06:46 PM   #14
ScottRiqui
Senior Member
 
Join Date: January 27, 2010
Location: Norfolk, VA
Posts: 2,905
Quote:
So what do you use to refer to the measurement from base to ogive?
I've never seen/heard a term or abbreviation for it. I'd suggest "BTO" for "Base to Ogive", but I'm not sure how useful a term it would be, unless there's an accepted standard for where exactly on the ogive to measure to.
ScottRiqui is offline  
Old March 31, 2013, 06:50 PM   #15
trobin
Senior Member
 
Join Date: February 26, 2013
Location: Louisiana
Posts: 115
Wouldn't it be the point on the ogive that makes bore diameter?
trobin is offline  
Old March 31, 2013, 06:52 PM   #16
ScottRiqui
Senior Member
 
Join Date: January 27, 2010
Location: Norfolk, VA
Posts: 2,905
Quote:
Wouldn't it be the point on the ogive that makes bore diameter?
That would make sense to me, but I don't know if every comparator out there uses the same point to make measurements.
ScottRiqui is offline  
Old April 1, 2013, 04:37 AM   #17
Mike / Tx
Senior Member
 
Join Date: April 8, 2000
Posts: 1,289
Quote:
trobin
Wouldn't it be the point on the ogive that makes bore diameter?
Quote:
ScottRiqui

That would make sense to me, but I don't know if every comparator out there uses the same point to make measurements.
If everyone used the same brand comparator is the big thing here.

Yes a comparator "should" measure to the area of the bullet's ogive that is the point that the leading edge of the "lands", (not the bore) will contact. I use the term "Base to ogive" (BTO) in my notes when referring to this measurement.

I use OAL when referring to the total overall length of the cartridge, which like you mentioned above, is usually used to determine the general lenght required to fit in and/or feed from a magazine.

With either of these however there are generalities that are fairly loose with regard to specific firearms.

If I am looking for an OAL, (base to tip) of a lead tipped bullet for instance, I usually will measure 5 loaded rounds of the specific caliber and the specific bullet being loaded, and average the readings to be used as my length in my notes. I will also jot down the BTO, (base to ogive) length as well as the tool I used to gather it.

I normally use the Stoney Point, (Hornady) set to measure with, however I also have a piece of barrel stub from my barrel, which was short chambered using the same reamer that cut the chamber for a custom rifle. It is an inch long and I can use it to seat my bullets to as close to exactly to my chamber as possible without actually seating the bullet in the rifle.

I am sure there are also many others out thee with similar type of tools which were either made from barrels like mine or possibly they are simply other brands. The end result however is that the reading you will get using any of them is only good for the specific chamber length of your firearm, and the bullet and brass brand, type, and caliber your loading at the time. Change any one of them and you are starting from scratch.
__________________
LAter,
Mike / TX
Mike / Tx is offline  
Old April 1, 2013, 06:57 AM   #18
SL1
Senior Member
 
Join Date: November 8, 2007
Posts: 1,999
I don't think that anything but confusion will result from defining any acronym that begins with a "C" as the distance from the cartridge head to the point on the bullet that is anything different than its tip.

Measurements with bullet comparators are useful FOR INDIVIDUAL RIFLES, but not as standards, because bullet contact with the rifling can occur at much different locations on the bullet, depending on how the beginning of the rifling is shaped with respect to how the bullet is shaped. And, the beginning of the rifling will erode over time, changing that relationship.

So, if you think that using a comparator to measure the distance from the case head to the beginning of the full-diameter part of the bullet is giving you the distance that will allow your bullet to just touch the rifling, you are probably misleading yourself by some unkown amount. On the other hand, if you use the gun itself to determine that distance, you will have a measurement that is useful FOR THAT GUN ONLY. Finding the measurement that YOUR bullet comparator gives you with a cartridge made-up with a particular bullet that just touches the lands will give you an easy way to monitor your ammo as it is produced, so there is some value in using a comparator.

But, there seems to be little value to us forum members swapping those particular length measurements. What we should swap is the DISTANCE OFF THE LANDS, which is often just called "bullet jump". That seems to have the most meaning with respect to peak pressure and accuracy, although matching it from gun to gun is not any guarantee for matching either peak pressure or accuracy from gun to gun.

SL1
SL1 is offline  
Old April 1, 2013, 10:56 AM   #19
Nathan
Senior Member
 
Join Date: July 1, 2001
Posts: 1,941
COAL or BTO are measured one way, but are usually discussed as [Touching the lands] -0.###.

I must have learned COAL wrong, but it works for me.

Those who believe base to tip OAL is critical for ballistics need to look at bullets more. Tips are where designers put bullet jacket variation. long range BR guys actually take the time to cut it square!
Nathan is offline  
Old April 1, 2013, 05:36 PM   #20
wncchester
Senior Member
 
Join Date: December 1, 2002
Posts: 2,832
OAL and COAL are generally considered the same thing; (Cartridge OAL is the same thing as Over-All Length). There is no standard name for 'comparitor' length. Case length is case length, there's no other name for it.

Of more significance is your photo method of measureing bullet run-out at the case mouth is mostly going to measure your bullet's roundness and that will usually be quite good. For a much better indication of what you want to know, put the tip of the dial indictor as near the meplat as you can get while staying on the jacket.

No one ever knows what Guffy's really talking about, mostly it's just talk.
wncchester is offline  
Old April 1, 2013, 07:14 PM   #21
Nathan
Senior Member
 
Join Date: July 1, 2001
Posts: 1,941
Quote:
Of more significance is your photo method of measureing bullet run-out at the case mouth is mostly going to measure your bullet's roundness and that will usually be quite good. For a much better indication of what you want to know, put the tip of the dial indictor as near the meplat as you can get while staying on the jacket.
That is certainly a fine idea, but my experience is that getting too close to the meplat only tells me if the bullet has runout, not if my reloading process does. I think the picture is showing measuring at the Ogive which is about where the seating die touches off and the bullet touches the lands. If you feel the picture is not good enough, maybe this description improves it some.

As for all of tha naysayers about OAL vs a distance into or from the lands, please suggest what to name this. If the discussion is more that this measurement is not as important, please look at the guys who setup loads to shoot 100 yard groups of .010" or something like that. Case fit to chamber and bullet distance into or from lands are their primary measurements. Maybe throw in how many clicks on the Harrels powder measure!
Nathan is offline  
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 01:26 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2014 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Contact Us
Page generated in 0.12980 seconds with 9 queries