Accuracy of OAL

Discussion in 'The Ammo & Reloading Forum' started by stev32k, Oct 31, 2012.

  1. stev32k

    stev32k Well-Known Member

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    I've trying set up the dies for 9mm and have been making dummy rounds all day. The target OAL (from the Hornady manual) is 1.075. I made four rounds and they were almost dead on target. They varied from 1.071 to 1.077. So I thought I would do a longer run to get a larger sample and something must have moved because the results are off. I attached the measurements.

    The question is what is a safe, acceptable deviation from the published data. I believe I can get them closer to target by working on the seating die if that is necessary.

    Attached Files:

  2. gdmoody

    gdmoody Moderator Supporting Member

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    You are never going to get them all the same length, no matter what you do. When you seat the bullet, even though the bullet seating die hasn't moved, the ogive (roundness of the nose) is going to be different. The die will seat them the same every time, it is just going to measure differently. It drove me crazy for a while until it was explained to me. I may not be making a lot of sense but some one will come along that can explain it better.

    You just want to make sure that they are less than the 1.075 inches or that they will fit in the magazine without any problems.
  3. 312shooter

    312shooter Active Member

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    :yeahthat:

    Trying to create a perfect, consistent OAL from the bullet nose is a nettlesome science which provides little relevancy to anything other than revealing the inconsistency of common bullets. If you are looking for consistency for any relevant purpose like accuracy, you should be using a comparator- engagement of the lands vs bullet ogive is the topic, bullet nose measuring is simply a starting point drawn from your loading data for establishing reliable function in your specific firearms. This is easily established by setting your seating dies to an average target COAL and loading them and function testing at the range, forgetting the .001 differences in the finished product will make this a much more enjoyable hobby when dealing with pistol rounds.
    Last edited: Nov 1, 2012
  4. steve4102

    steve4102 Former Guest

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    Good advice above. Your OAL variance is fine, more important will your OAL fit-feed-fire in YOUR pistol.
    OAL is bullet and firearm specific not manual specific.
  5. stev32k

    stev32k Well-Known Member

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    Thank you for the replies, but I my question still is how much deviation from published data is acceptable? Hornady calls for an OAL of 1.075, Lyman 1.090, and Lee 1.125. That is a pretty good spread. I've read that the bullet should never touch the powder charge so it seems to me that longer is better up to a point.

    What is the limiting factor in bullet setting depth? Is it the chamber size of the gun or the amount of the bullet that is inside the case, both, or something else? Sorry for all the questions, but I can't seem to find the answer in any of the books I have on or on the internet.
  6. steve4102

    steve4102 Former Guest

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    Where did you read this? Certainly not in any reloading manual. Not only is it safe for the bullet to touch the powder it is safe for the bullet to compress the powder. Providing there is load data to support the charge of course.

    Here is a blog that may help answer some of your OAL question.

    http://glocktalk.com/forums/blog.php?b=256
  7. LDBennett

    LDBennett Well-Known Member

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    A couple of things:

    Bullet nose shapes

    The length of the finishes cartridge from the OGIVE to the base is what counts not the Over All Length (OAL). We want every cartridge to have the same amount of travel to get into the bore of the gun and the first point that engages the bore is on the ogive of the bullet nose. So to measure the accuracy of the bullet seating, we need to use a tool that touches the ogive rather than using the cartridge OAL. That tool is called a comparator. Here are a few:

    http://www.midwayusa.com/find?userSearchQuery=comparitor

    Mass produced bullets are not all that accurate in the exact shape of the ogive because of the way they are made. You can get better bullets but for handgun ammo it is a waste of money as handguns can only be as accurate as you can shoot them and regular bullets probably exceed most all of our abilities to shoot them.

    Over all cartridge lengths

    The most important thing is for the rounds to fit the magazine, feed well, and fit the chamber without resistance. The OAL listed in the manuals are such that they should fit ANY gun made to the industry specifications (is it SAAMI?). If you choose another OAL that meets this criteria do start at the starting load level and work up, not exceeding the max load level of powder and watching for pressure signs. Be aware that the shape of the ogive may change between bullet manufactures so make sure that any ammo you reload fits the gun.

    Usually lighter bullets are loaded shorter in the cases because they are shorter in and of themselves. There is a certain amount of the body of the bullet that has to be inside the case to assure the bullets will not fall out with handling or when pulled and jerked through the feeding operation of the gun. So... just set up the seating die per the book and don't worry about the OAL after that and make the rest of the batch. For handguns anything more in controlling the OAL is a wasted effort. Random checks of the OAL is wise to assure the dies have not lost their adjustments but that only need be within several thousandth for the same bullets from the same manufacturer's lot. The bullets might change shape slightly from lot to lot and if they are bulk bullets then they may change lots within the same bag of bullets. This OAL length is not critical as long as you stay with the reloading manual specs plus or minus several thousandths. The comparator measurements should turn out to be within a few thousandths.

    Hope this helps.

    LDBennett
  8. stev32k

    stev32k Well-Known Member

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    Maybe I'm wrong (wouldn't be the first time), but I thought I remembered reading it in one of the reloading manuals. I'll have to go over it again.
  9. LDBennett

    LDBennett Well-Known Member

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    stev32k:

    There are some powders that only work well with a completely full case in which the powder easily touches the back of the bullet. Some powder loads end up against the back of the bullet (partially at least ) when the gun is elevated for shooting horizontally. Some loads work best if you actually compress the powder when you seat the bullet. Now, I don't use compressed loads because the compression force may eventually push the bullet out of the case somewhat making consistence of the reloading process hard to maintain and accuracy can suffer.

    Anyway, it is OK for the powder to touch the back of the bullet. But it is not OK to make up loads with more powder than in the recipes in reloading manuals.

    LDBennett
  10. PanhandlePop

    PanhandlePop Member

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    You are really over-thinking this issue. Trying to match specifications in your reloading manual is a good idea, especially when learning, but isn't always possible because of component availability.

    The deviation shown on your table for the length you selected is not unusual or cause for concern. Beyond that, OAL in manuals should be treated as guidance, not gospel. Different manuals show data based on different bullet makes and designs, different cases, and their particular testing protocol. Some will just show max OAL. The key to OAL is to find what fits (plunk test) and cycles through YOUR firearm. You should be able to safely load to a longer OAL than shown in your manual (keeping at or under SAAMI specs), but realize that, at starting charges, the round may not cycle the pistol reliably. You also can go with a shorter OAL than shown in a manual but you should adjust (lighten) the powder charge to account for less case volume/higher pressure.
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