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Old December 7, 2012, 12:28 AM   #1
TheDutchman19
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COL - What all does it do?

OK, here is a newbie question, from a guy who is trying to grab all the info I can about my new hobby.

The last week, I have been setting up new dies for my 30/06. I had planed to use a IMR product with a 125 gn bullet, which called for a COL of 3.080. Due to availability, I end up with a comparable Hodgdon product. The Hodgdon was not in the load book I was using, so I grabbed another. With the same bullet the other book had a COL of 3.150 and the powder charge was different for the IMR

I understand that different load data calls for varying COL depending on the powder charge. With the same bullet, a shorter COL and the same powder will usually call for less powder. I assume the shorter COL has less volume in the cartridge and less powder is needed to build up pressure.

What are the pros and cons between them:
Shorter COL - more surface area for the neck to hold the bullet?
Shorter COL - bullet is farther away from the barrel verse the longer COL being closer?
More cartridge volume with more powder verse less volume with less powder?

Please help explain the differences. Thanks
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Old December 7, 2012, 12:52 AM   #2
Shotgun693
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The COL can effect the way a bullet loads into the chamber, especially in an auto but also in a bolt action and a lever action. Yes, the distance from the lands effects pressure and accuracy. The volume of the case is effected. A heavier bullet is, as a broad rule, loaded longer than a lighter bullet. The length of a box magazine can set the maximum COL of a round. The shape of a bullet and if it has groves for lube can effect COL. A bullet with a crimping grove needs less neck held by the case neck.This is just the tip of the iceberg. Read, read, read. The slower the burn rate of the powder the more volume it generally has the more you might need to load longer. The faster the powder burns the less is normally used and the bullet can, if need be, loaded shorter.
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Old December 7, 2012, 12:56 AM   #3
tkglazie
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Pretty much every aspect of reloading gets rolled into a good reply to that question. The only way you are going to get the answer that you think you want is to start from scratch and bone up on the physics of reloading and the relationship between your cartridges and the chamber of the specific gun that they will be used in.

The best way to learn what you want to know is to read two different loading manuals from beginning to end. My two favorites are the ABCs of Reloading and Lee's Modern Reloading 2nd Edition. The front of each will provide all the info you are looking for. Others prefer Lyman's 49th, this is also a great resource.

Bottom line is there is no pro or con to a shorter or longer COL, per se. For example- shortening the COL with a given charge in your 30-06 cartridges does increase the pressure, as you pointed out, but at the same time, by shortening the COL you are moving the bullet away from the rifling and giving it more of a "headstart" before it enters the barrel which results in a reduced pressure. Trippy stuff.

Understanding the nuance of the effect of COL changes on the accuracy (and safety) of the finished cartridge is key to good rifle handloading. Once you have a solid grasp on the forces at play from the time the primer fires to the time the bullet leaves the barrel (and a little bit beyond that) you will have answered your question.
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Old December 7, 2012, 01:00 AM   #4
TheDutchman19
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Shotgun693, could you recommend some good resources if I am trying to dig a little deeper?
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Old December 7, 2012, 07:19 PM   #5
wncchester
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"I had planed to use a IMR product with a 125 gn bullet, which called for a COL of 3.080."

Not quite true. What the data shows is the OAL the testers used but it's no more a 'rule' for anyone else than their powder charges.

There is precious little difference in the basic beginner level loading instructions found in reloading manuals. They just use slightly different words and illustrations to convey the same fundamental information.

There are precious few books (or magazines) that give intermediate level info. The best books I've found are Fred Sinclair's (Goggle Sinclair International) instruction book and the excellant Precision Shooting Reloading Guide which is often listed in the Sinclair catalog.

The few other popular books for competion reloading are of some benefit IF you're loading FOR competiotion (usually with a .223 or .308 autoloader) or maybe serious BR stuff; meaning little of that stuff applies to what most of us need help with.
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Old December 7, 2012, 08:15 PM   #6
scsov509
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Quote:
What are the pros and cons between them:
Shorter COL - more surface area for the neck to hold the bullet?
Shorter COL - bullet is farther away from the barrel verse the longer COL being closer?
More cartridge volume with more powder verse less volume with less powder?
You've already gotten lots of good ideas, and I'd echo some of what has been said. I'd add in terms of pros that generally speaking a longer COAL is going to give better accuracy, because by getting the bullet closer to the lands it's going to also engage the rifling more concentrically. At the same time, too long will put you into the lands which is can be dangerous in terms of creating a pressure spike. So what manuals do is provide a COAL that will typically be safe in all rifles, but not one necessarily that's ideal for any given rifle.

So it's helpful to find how long you can go in your specific rifle. As mentioned, anything magazine fed will have a max length that's going to fit into the magazine, and sometimes that magazine length will be as long as you can go. Other times a mag will still allow you to seat out long enough to get to the lands, and if so I find my best accuracy is generally .010-.015" off the lands.
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Old December 7, 2012, 08:50 PM   #7
tkglazie
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Quote:
You've already gotten lots of good ideas, and I'd echo some of what has been said. I'd add in terms of pros that generally speaking a longer COAL is going to give better accuracy, because by getting the bullet closer to the lands it's going to also engage the rifling more concentrically. At the same time, too long will put you into the lands which is can be dangerous in terms of creating a pressure spike. So what manuals do is provide a COAL that will typically be safe in all rifles, but not one necessarily that's ideal for any given rifle.

So it's helpful to find how long you can go in your specific rifle. As mentioned, anything magazine fed will have a max length that's going to fit into the magazine, and sometimes that magazine length will be as long as you can go. Other times a mag will still allow you to seat out long enough to get to the lands, and if so I find my best accuracy is generally .010-.015" off the lands.
Wow. Those two paragraphs are about as well written as any I have read on the subject. Well said.
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Old December 7, 2012, 10:10 PM   #8
Shotgun693
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I'd recommend going to a used book warehouse, buy every book you can find on reloading and ammo in general. I've been reloading, mostly for revolvers, for over 35 years. I can't quote sources for some of the stuff I know because I just don't remember. For general info on Ammo read a copy of 'Cartridges Of The World'. BTW, while starting out go by a current reloading book. Start well under a max load.
Here's a little tip. Say you want to load a 150 gr bullet for a .308, take a factory .308 round and set your dies to match this, now with a load well under the max you ought to be just fine. As you learn more you can experiment more but go slow and make small changes.
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Old December 8, 2012, 05:31 AM   #9
scsov509
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Wow. Those two paragraphs are about as well written as any I have read on the subject. Well said.
Thanks for the kind words, it's always nice to be able to contribute something helpful after I've learned so much through the years from so many others.
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