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Old 02-03-2012, 12:10 PM
Bromel Bromel is offline
 
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Default Special tools to measure cartridge overall length (COAL)?

I was reading something online today and saw a reference to a special tool that can be used in conjunction with calipers to more accurately measure the overall length of a cartridge. It measures from a point on the ogive instead of from the tip of the bullet. What is this tool called? Is it useful? And, if so, where can I buy it?
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  #2  
Old 02-03-2012, 12:34 PM
pmclaine pmclaine is offline
 
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Bullet comparator? I think Hornady sells one, it may be referenced as a formerly Stony Point item. If you check Sinclairs online catalog you will find some of these offered by other manufactures. It clips on to your caliper with a set screw. If you decide to get one of these you may also want to get a second et of calipers you could dedicate for use with the comparator.

I think it would be useful if you want to ensure the best measurement of breech face to bullet bearing surface. This would be important if setting up your bullet to the tightest measurement just of the lands of the barrel. If you think your rifle can take advantage of it its a good tool. Ive just loaded my first rifle ammo and what I am finding is out of the box meplats are not all that uniform. Measuring from base of bullet o meplats will give variances in COAL.

Hornady/Stony Point also makes a nice tool to measure ideal COAL using a modified rifle case that allows you to use the bullet of your choice to find best seat based on ogive contact with lands in your rifle. Take a look at that also while shopping.

By the way I own none of these but would do so if I wasnt sepnding money on other stuff.

Last edited by pmclaine; 02-03-2012 at 12:40 PM.
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  #3  
Old 02-03-2012, 01:18 PM
musketjon musketjon is offline
 
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Another way to check your OAL is to load a bullet purposely long in the case. Completely chamber the round carefully. Carefully extract the round from the rifle (hopefully the bullet doesn't stick in the throat). You should see the rifling starting to imprint on the front of the bullet. Set your seater die until it just touches the bullet in the press. Turn the seater plug in about 1/4-1/2 turn more. That should give you a really good starting point for finding your rifle's maximum chamber length. Make sure the round will fit in the magazine ok. If it does and you're feeling ok with it, load to your heart's content. No special tools needed. Remember, the gage is just that--a gage. It won't help seat the rounds to any more consistant oal than your seater die is capable of. M1's are not 1/4 minute-of-angle guns and a few thousandths of an inch oal one way or the other won't make a hill of beans of difference.
Jon
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Old 02-03-2012, 01:26 PM
Bromel Bromel is offline
 
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Quote:
Originally Posted by musketjon View Post
Another way to check your OAL is to load a bullet purposely long in the case. Completely chamber the round carefully. Carefully extract the round from the rifle (hopefully the bullet doesn't stick in the throat). You should see the rifling starting to imprint on the front of the bullet. Set your seater die until it just touches the bullet in the press. Turn the seater plug in about 1/4-1/2 turn more. That should give you a really good starting point for finding your rifle's maximum chamber length. Make sure the round will fit in the magazine ok. If it does and you're feeling ok with it, load to your heart's content. No special tools needed. Remember, the gage is just that--a gage. It won't help seat the rounds to any more consistant oal than your seater die is capable of. M1's are not 1/4 minute-of-angle guns and a few thousandths of an inch oal one way or the other won't make a hill of beans of difference.
Jon
Thanks for the responses. I also recently acquired a Finnish M39 Mosin Nagant, so I might get the tool for that purpose.
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  #5  
Old 02-03-2012, 01:34 PM
mousegun mousegun is offline
 
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COAL is the measure of meplat (bullet tip) to case head. A good caliper is all that's necessary for this. Set the caliper to the COAL measurement (ostensibly 3.34 inches for the Garand rifle). Any cartridge which will pass through the jaws of the caliper will not hang up in the Garand magazine.

The bullet comparator will measure from the case head to a point on the ogive corresponding to the bore diameter of the barrel. This measurement allows a reloader to set the seating depth of the bullet to achieve a desired clearance of the bullet's contact with the lands of the barrel. This is not a particularly useful measurement for Garand ammunition since bullet seating should be chosen not to exceed a length that would impede the action's loading of the cartridge. In most cases this length will not allow further refinement of bullet seating.

For what it's worth, I use one of these with a caliper for my other rifles (.243 and 7.62x54r).
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Last edited by mousegun; 02-03-2012 at 03:37 PM.
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  #6  
Old 02-03-2012, 01:41 PM
Bromel Bromel is offline
 
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Quote:
Originally Posted by mousegun View Post
COAL is the measure of meplat (bullet tip) to case head. A good caliper is all that's necessary for this. Set the caliper to the COAL measurement (ostensibly 3.34 inches for the Garand rifle). Any cartridge which will pass through the jaws of the caliper will not hang up in the Garand magazine.

The bullet comparator will measure from the case head to a point on the ogive corresponding to the bore diameter of the barrel. This measurement allows a reloader to set the seating depth of the bullet to achieve a desired clearance of the bullet's contact with the lands of the barrel. This is not a particularly useful measurement for Garand ammunition since bullet seating should be chosen not to exceed a length that would impede the action's loading of the cartridge. In most cases this length will not allow further refinement of bullet seating.

For what it's worth, I use one of these with a caliper for my other rifles (.243 and 7.62x54r).
Thanks, I was considering that tool. But what's up with the link to the internet troll???
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  #7  
Old 02-03-2012, 01:48 PM
raymeketa raymeketa is offline
 
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Most guys don't like to hear this but . . . getting anal about base to ogive measurements when dealing with military and/or factory rifles is usually a waste of time. OAL length is important when loading from a magazine but the distance off the lands seldom is. Even when you are shooting the super accurate benchrest rifles (I do) adjustments in length result in only small improvements in accuracy. But, Benchrest is a game of small groups and any improvement in accuracy, even if you can only measure it in thousandths of an inch can be the difference between first place and first loser.

Practice, practice, practice will usually result in more improvement in your groups and scores than any gizmo you can buy.

JMHO

Ray
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  #8  
Old 02-03-2012, 02:57 PM
USSR USSR is offline
 
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Quote:
Originally Posted by raymeketa View Post
. . . getting anal about base to ogive measurements when dealing with military and/or factory rifles is usually a waste of time. OAL length is important when loading from a magazine but the distance off the lands seldom is.
Ray's correct. I have and use the bullet comparator shown by mousegun, but not for normal rifle loads, and certainly not for Garand loads.

Don
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  #9  
Old 02-03-2012, 03:35 PM
mousegun mousegun is offline
 
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Quote:
Originally Posted by Bromel View Post
Thanks, I was considering that tool. But what's up with the link to the internet troll???
Oops! Was from another posting. I'll correct it. Was supposed to go to the Sinclair site. Check back a few minutes after the post time here and it should be OK. If not, check here.
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  #10  
Old 02-03-2012, 03:49 PM
mousegun mousegun is offline
 
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Quote:
Originally Posted by raymeketa View Post
Most guys don't like to hear this but . . . getting anal about base to ogive measurements when dealing with military and/or factory rifles is usually a waste of time. OAL length is important when loading from a magazine but the distance off the lands seldom is ....
JMHO

Ray
I could not agree more. But for my style of handloading consistency is important. I have several nose styles and weights of bullets for some calibers (e.g. 60gr/80gr/85gr/100gr for .243) which don't always seat to the best depth for optimum loading at one seating stem setting. Instead of keeping dummy cartridges around for each bullet, I keep notes on length and can thus reset the seating stem appropriately. However, that's my way. YMMV.
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