Measuring COAL


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Wildyams
September 8, 2011, 02:06 AM
I just found this product at Midway "Frankford Arsenal Cartridge Overall Length Gage"

and in the description it makes the device sound absurdly simple.. I could probably put something together that would work just as well. My question is, does this sound like a good method of determining a max COAL?

"Directions:
Install the appropriated caliber size tip on the end of the cleaning rod (sold separately)
Insert the cleaning rod down the barrel until there is contact with the bolt face then install one clamp
Remove the bolt and drop a bullet (projectile only) into the chamber
Hold the bullet against the rifling with a pencil, touch the bullet tip with the cleaning rod tip and install the other clamp
Now measure the inside distance between the two clamps with calipers(sold separately) and record the measurement
The measurement taken can be used as a gage to check the seating depth setup during the reloading sequence and will tell you the maximum length you can seat bullets until the hit the lands of the rifle barrel"


http://www.midwayusa.com/viewproduct/?productnumber=190644&cm_vc=S015


Thoughts?

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Canazes9
September 8, 2011, 07:28 AM
It is clever, but I have difficulty believing it would be precise enough for measuring something as critical as COAL. I would never be able to trust it and would always feel the need to verify the measurement w/ a bullet in a case. I have no use for it.

David

fguffey
September 8, 2011, 07:29 AM
I would not do it that way, some just use a stick, mark it with a pencil with little regard to the width of the pencil mark and the fact the tip of the bullet is not a datum, so I would suggest you try what others do, measure from the contact point between the bullet and barrel, the contact point is/will be between the large and small diameter of the barrel, in the perfect world and if we were talking about 30/06 the contact point would be between .300 and .308 then if it is possible to consider the contact point is a cone with varying diameters one should consider the contact point does not move, ever though there are those that find it necessary to find it everyday.



Me? I drill the flash hole, I am a big fan of bullet hold, I seat a bullet, remove the bolt, chamber the test case, then push the bullet out of the case with a cleaning rod until it contacts the rifling, then stop, with bullet hold I use the test case as a transfer, I transfer the dimensions of the chamber to the seater die, no Hornady gage, no Sinclair gage, no Frankford gage with one end sitting against the tip of the bullet and I refer to the length of the assembled cartridge as OAL.

Add: maximum, if we are talking about maximum length as in too long for the 'box' I use the dial caliper, most of my work is accomplished with the feeler gage and the dial caliper...and datums, I use datums.




F. Guffey

243winxb
September 8, 2011, 08:29 AM
Seems you could take the same measurement with a regular cleaning rod & 2 pieces of tape??

Wildyams
September 8, 2011, 10:47 AM
Seems you could take the same measurement with a regular cleaning rod & 2 pieces of tape??

Thats what I was thinking...

I think I'll give it a try, see what number it gives me and try a few other methods and compare the numbers. I don't think that will hurt anything at all. haha

rcmodel
September 8, 2011, 11:09 AM
I leave all the expensive measuring tools & Chinese algebra to others.

I just seat it long, then use a birthday candle to smoke the bullet ogive.
Try to chamber it, and the rifling leade will rub off the smoke.
Keep seating slightly deeper, and smoking the bullet again, until it doesn't.

That right there is as close to exact as anyone can measure by any method.
And the cost for the "tool" is certainly right!

BTW: A Dry Erase black marker works as well if you don't have a birthday candle.

IMO: If I just had to buy something, I'd buy a universal Bullet Comparator so you can actually measure something meaningful as far as COL goes. (Instead of measuring off the bullet point, which is not at all the same each bullet)
Works with your plain old digital or dial caliper.
http://www.sinclairintl.com/.aspx/pid=34262/Product/Sinclair_Hex_Style_Bullet_Comparators

rc

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