Help understanding COL and why so many differences?

Discussion in 'The Ammo & Reloading Forum' started by prof_fate, Feb 10, 2012.

  1. prof_fate

    prof_fate Former Guest

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    I thought the COL of a 9mm was 1.169...
    I"m looking at various reloading data and the COL varies a lot...I don't have enough info to understand why.

    I assume it has to do with how much volume is in the case but since cases can vary in volume i'm not sure that's the reason.

    I know a hollow point may be different than RN and a 90gr would (or could) be different a 147g bullet...but that's not consistent at all either.

    I've seen 1.09" COL up to 1.150 and nothing up to 1.169.

    I've read that brass can vary in length a good bit as well (.743 to .754) and if the headspace is determined by this then it's gonna be all over the place...

    So....why the difference in COL and what does changing it do? I've measure factory ammo and it varies a wee bit from bullet to bulet (.005 or so)
  2. The_Rifleman

    The_Rifleman New Member

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    Mostly I think it is bullet construction. My Hornady manual lists the smallest bullet at 1.07, and the largest/heavies bullets 147gr, at 1.1 and 1.165. I would think there is a specific length that you don't want to exceed to insure the ammo cycles smoothly.

    [edit]I should have included: they probably want a specific amount of case contact on the bullet to provide tension to hold the bullet in place. So the cartridge with a smaller bullet will have a shorter length.[/edit]

    I reload for a 25 auto, I seat them a bit longer than what the book says, and that aids in smoother operation.
    Last edited: Feb 10, 2012
  3. prof_fate

    prof_fate Former Guest

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    Well ran the press around and got 4 made. Formula calls for 1.125...first two are at 1.130 and then a 1.120 and a 1.125....probably not the best for accuracy but I"m just testing to see if all works or not.

    Using a 4.2gr load when the formula runs 3.9 to 4.4. Low end FPS is 1009 and high end 1086 which isn't much,but pressure spread is 25,700 to 31,200. Intesting that a 21% jump in pressure only gets you 7% more velocity.
  4. steve4102

    steve4102 Former Guest

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    1.169 is Max OAL for the 9mm, it is not THE OAL.

    OAL is not manual specific or even bullet specific, it is firearm specific. The round must first fit and feed in your firearm. Find the OAL that best fits and feeds with your choice of bullet then "Start Low and Work Up. After all, if it doesn't fit,feed and fire there is no need to be concerned about pressure.
  5. todd51

    todd51 Well-Known Member

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    I agree with Rifleman and Steve. The data you see in the manual is from a specific bullet from a specified manufacturer. You will find differences even with the same weight and bullet profile between different manufacturers,even slight differences from the same batch of bulk bullets. A 115 gr. fmj bullet from say Remington will have a slightly different profile of a 115gr. fmj bullet from say Winchester or Mag Tech or any of the other manufacturers and this will lead to a different over all length. When starting out with new components and working up a load, make up some dummy rounds with just case and bullet seated and cycle them through for function and feed and check for proper head space, and just till you have what you want before loading up the finished product.
  6. 312shooter

    312shooter Active Member

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    Understanding OAL is enough to make you head spin I suppose. I use the Lyman 49th for my primary source of load data. The first page of data relating to the cartrige you wish to load for with the exploded cartrige view displays the absolute MAXIMUM OAL for any loading of that cartrige. When you go to a specific bullet style and weight you will find the Minimum or "do not seat shorter than" length in the upper corner. Somewhere between these two measurements lies an ideal OAL for your firearm. Looks like your OAL is exactly where I seat my 115gr RN bullets-1.130" Other than that I let all the pressure testing to the guys in the lab, who have alot more safety precautions in place than I do. YMMV
  7. prof_fate

    prof_fate Former Guest

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    Dummy / test round questions..


    I did that more to check die set up than gun feeding. I have a Lee factor crimp die for crimping and it also does an overall size. I used a lead bullet. I took it apart and now the bullet it undersize - it will sit too far into a flared shell.

    Is this normal? Is my die set wrong? The bullet is supposed to be .356 - and the unused ones are, but this 'used' one is more like .354.
    Last edited: Feb 11, 2012
  8. todd51

    todd51 Well-Known Member

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    All my jacketed 9mm bullets (several different mfg and styles) are marked/advertised as .355 but they all measure .354 with my calipers. I am presently loading Winchester 124gr. fmj for range plinking. They measure .354 with my caliper also. Just to be sure of what is going on I just pulled one and it still measures .354. I also use the Lee factory crimp die and am crimping to .375. I have never loaded lead bullets in 9mm so don't know what might be going on.
    Last edited: Feb 11, 2012
  9. prof_fate

    prof_fate Former Guest

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    I may have something mis adjusted.

    Reset every die and checked everything...getting 1.140 to 1.145..not sure why the variation. Could be variances in the cast bullets or case length (speer bullets, once fired brass of mixed brands).

    Not sure how much this variance will affect anything.
  10. todd51

    todd51 Well-Known Member

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    It is normal for my reloads to vary up to .005 in COL using new sized brass of the same mfg. and the same bullets. I load 124 gr. fmj to a COL of 1.122 and it is not uncommon for some to measure up to 1.125 or down to 1.121. I have also found factory ammo to vary those few .000s and have considered it normal.

    I size all my new brass. If I don't I can many times push the bullet down in the case with my finger. After I size it that is not the case and can only set it into the flare/bell.

    I went down to the loading room and checked my supplies and found some really old Speer 125gr. lead round nose. The factory package said dia. of .356 but my calipers measured them at .354. I loaded one in a new case and then pulled it. I had been swedged down to .353.

    Variations in case length are not going to effect the COL of you finished round. It will effect how much of the bullet is in the case though.

    I don't push the upper end of loads so I don't think these slight variances will effect any thing. If you are pushing the limits pressure wise then they could be a problem.
  11. The_Vigilante

    The_Vigilante New Member

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    A Lee Factory Crimp die will resize your bullet (lead) as well as the case. There's really not much you can do about it. Resize the case, if it still drops in then sell the bullets as scrap or to one of your reloading friends who casts his own bullets.
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