Different COL with different bullets?


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JonB
November 24, 2007, 10:19 PM
Hi guys - something I stumbled on earlier today. How come there are different COL for different bullets in the same caliber? ie looking at the Accurate reload data for 10mm, some of the bullets say 1.25 COL, some say 1.26, and I think there was even a 1.245. What gives?

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ReloaderFred
November 24, 2007, 10:30 PM
A lot of it has to do with the shape of the bullet. The ogive of the bullet determines the loaded length, in some cases. There has to be enough freebore for the bullet to release some of the pressure before starting down the bore. A long ogive bullet will have a longer OAL than a short ogive bullet. Another determining factor is whether or not the round is going to feed through a particular magazine.

All bullets aren't created equal when it comes to shape. Hence the different OAL measurements.

Hope this helps.

Fred

strat81
November 24, 2007, 10:41 PM
Heavier bullets are generally longer bullets. That length has to go somewhere.

JonB
November 24, 2007, 10:56 PM
OK makes sense. But 5 thousandths of an inch difference? Seems like such a small amount that it wouldn't matter. I'll have to read up on 'ogive' - new term to me. I have been trying to get the COL close, but can't get each one to exactly match the published specs. I shoot a Glock which are known for reliability so I am guessing they may be a little more forgiving of a few thousandths of an inch.

FieroCDSP
November 24, 2007, 11:26 PM
Please be very aware (especially if you're using max or near-max loads) that seating two different lengths of bullet to the same cartridge OAL is going to increase the pressure in the longer bullet. As stated above, the bullet has to go somewhere. Many bullet manufacturers publish a load data book for their bullets. Some, like Rainier and Berry's are fairly similar and can be interchanged on occasion(also because they use mid-loads). Others are very different and should not be interchanged.

Thus why many of us have at least three load-books floating around.

ReloaderFred
November 25, 2007, 01:15 AM
The ogive is the curve of the bullet's nose. Some bullets have long ogives, like the 9mm NATO design, while others have short ogives, like flat point bullets. The point on the curve that actually contacts the rifling, or leade, has a bearing on how deep the bullet is seated in the case. When you seat a bullet deeper, you also reduce the volume of the case, which in turn increases pressure, if the powder charge remains the same. There must be a gap between the bullet and the contact point, or pressures will spike, sometimes dangerously.

Hope this helps.

Fred

JonB
November 25, 2007, 10:35 AM
Great help guys - thanks! I'll work on getting them as close as possible. I don't use max loads - more in the medium-low range for my Glock.

Thus why many of us have at least three load-books floating around.

Agreed - I have found quite a few discrepancies between load data sources. I also picked up the 'Complete guide' for the calibers I have started to reload.

Thanks again guys.

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