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Overall cartridge length

This is a discussion on Overall cartridge length within the RAMMAC forums, part of the Gun Professionals category; Hello, Ive been starting to reload for my m14 and Ive noticed a lot of people use different COAL for their reloads. My lyman reloading ...


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Old May 30th, 2013, 08:51 PM   #1
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Overall cartridge length

Hello,

Ive been starting to reload for my m14 and Ive noticed a lot of people use different COAL for their reloads.

My lyman reloading manual says that 150gr COAL should be 2.735".
I see a lot of other people have been using 2.800 and in between the two for 147/150/155gr.


Here is my current load for my 18.5" barreled Norc m14

Hornady 150gr SST
Winchester commercial case
IMR4895 41 - 43 ( Have to find the right charge for my rifle)
CCI #200 primers
Case trim length 2.008
COAL - Im not sure about

Is there any disadvantage / advantage to having a larger COAL?

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Old May 30th, 2013, 09:36 PM   #2
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Cartridge Overall Length (COAL) is a balance between two primary things,

Accuracy
Mechanical Operation

Bullet shape and dimensions can effect how much volume there is inside the loaded cartridge. Hornady rifle bullets, for example, usually take up more space inside the case as compared to other brand bullets of the same weight. Therefore, Hornady bullets that are seated to the same depth as another brand bullets, of the same weight, will produce higher pressures and velocities. Some bullets with different shaped ogives (the area where the bullet's diameter starts to become smaller) will cause you to have to adjust the seating depth one way or another (longer or shorter) in order to optimize accuracy. Rifles with detachable magazines can force you to have to seat the bullet deeper so that it will clear the front of the magazine.

If a manual recommends a longer COAL than another manual, using the same bullet weight, then the longer cartridge will, quite often, have more mass seated inside the case or the ogive is shorter, or both.

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Old May 30th, 2013, 10:17 PM   #3
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I see. Still a bit indecisive about what I should seat to.

What would you recommend for the SST?

The info I got was from a Lyman 48th Edition.

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Old May 30th, 2013, 11:29 PM   #4
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2.74".

I have a copy of Hornady's 9th Edition manual and while they don't show a load any lighter than their 155gr Amax bullet for the M1A rifle, they do show a 150gr SST load for a Winchester model 70 in .308 Winchester. They recommend 2.74" for the model 70 load and I see no reason why you shouldn't use that length. I would also recommend not going much more than 44 grains of IMR 4895 for a top end load.

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Old May 30th, 2013, 11:33 PM   #5
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Thank you very much for the information.

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Old May 30th, 2013, 11:39 PM   #6
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I forgot to mention one other aspect that should be considered when trying to determine a good seating depth, neck tension; especially for the M1A semi-auto.

The deeper the bullet is seated the more neck tension there will be, more neck tension helps ensure that the bullet wont move under recoil. I like to have about one bullet diameter of shank length seated in the case (at least .308" seated with a .308 caliber cartridge). With the 150gr SST you could seat the bullet as far out as 2.867" and still have at least .308" of the bullet inside the case, but, the cartridge would be too long for the magazines (about 2.84" is as long as most mags will allow). So you could use a COAL of 2.74 - 2.84 inches. Adjusting the seating depth will effect the accuracy to some degree but you have experiment to find the best length for your rifle and cartridge. I'd start at 2.74" and test for group size and accuracy. Then I'd make a couple of ten rounds batches using 2.80" and 2.84" and see which COAL gave me the best groups and accuracy, then I'd stick with that COAL.

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