OAL Question

Discussion in 'Reloading' started by 1CouesHunter, May 18, 2009.

  1. 1CouesHunter

    1CouesHunter Active Member

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    I am having a hard time Understanding how to Properly use the Hornady OAL gauge. I was given dimensions 3.725" base to Ogive measurement with a 200 gr. Nosler Accubond on a 300 RUM case. Can someone Please tell me what the
    tip-to-base measurement would be? And the difference?

    Thanks!!
     
  2. BountyHunter

    BountyHunter Writers Guild

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    If you are saying someone "gave" you that figure, it is not accurate for your gun.

    That is off their gun, you need to get the measurement off your guns info.

    Sounds like you do not have the instruction sheet, go to the Hornady site and download it. Look in the sinclair catalog for it also. www.sinclairintl.com and on their site they have it posted and other ways to measure the info you need.

    Base to ogive is normally from the base of the bullet to where the comparator you must have hits the bullet ogive. Generally speaking the transition point from tapered to cylindrical on the bullet. Not quite but close enough to visulize. the ogive is where the bullet meets the rifling IF it was seated long and shoved in the chamber.

    Base to tip is the length of the bullet overall. That will be needed for Cartidge OAL or COAL to tell you how long a bullet and case can be to be in the magazine of the gun.

    Key to getting proper measurements and using them long term is to keep the same bullet for use time after time. I keep mine in little plastic tubes with labels saying which bullet and gun they go to.

    Bullets will vary from base to ogive within a box of 100. We have seen variances of up to .013 but anything under .003 consistently is very good.

    Here is a simple way to see this. Take a sized case and mill a slot in the neck almost to bottom of the neck with a dremel tool or fine metal saw. Seat a bullet in the case very long. take a black magic marker and coat the bullet sticking out of the case. chamber the round, it will go in hard and then slowly pull the cartridge out. Now take a magnifying glass and look for "marks" on the bullet. That is where the ogive is . If you try to measure the length of the marks you will find that they are from .030-.050 normally. That means you are "jammed" into the lands at least that far in order to leave a mark.

    Quite a few guys use that method also and just back off at least .010 past the length of the mark to where they are "just touching".

    BH
     

  3. 1CouesHunter

    1CouesHunter Active Member

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    Thanks for the Explanation, It is Based on My Gun. I would really like to know what 3.725" base-to-ogive computes to tip-to-base OAL. That would save me
    some time until I understand the tool.

    Thanks again all!
     
  4. BountyHunter

    BountyHunter Writers Guild

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    First off it doesn't compare.

    The standard definititon for "base to ogive is off the bullet alone. You are giving a bottom of cartridge to bullet ogive measurement it looks like.

    COAL is from bottom of cartridge to tip of bullet and that is used to determine max mag length of a cartridge to fit in a mag, regardless of ogive.

    Tip to base OAL is normally the total length of the bullet from the base to tip (no case).

    go to this article and read it for full explanation of how to. http://blog.sinclairintl.com/category/how-to-articles/

    BH
     
    Last edited: May 18, 2009
  5. boomtube

    boomtube Well-Known Member

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    OAL for a rifle load that feeds from a magazine only matters that it feeds properly. Your chamber ONLY cares for where the moving bullet strikes the rifling, it doesn't know or care how much further any other part of the bullet sticks into empty barrel space so OAL for accuracy isn't the correct concern.

    Bullets vary in lenght, base to the tip. The point of rifling contact on the ogive's curve is the important part, not the tip, so that's what we use as the seating reference for best, or at least most consistant, seating. And the best seating-contact length varies a lot, rifle by rifle and bullet by bullet.

    Trying to get consistant OAL's from base to the tip will lead you on a merry chase!
     
    Last edited: May 18, 2009
  6. woods

    woods Well-Known Member

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    The case length of the 300 RUM from the case head to the case mouth is 2.850". The Hornady OAL comparator attachement which measures to the ogive is almost exactly 1.000"

    [​IMG]

    With a bullet in the modified case (yes, there is a bullet in there) and placed against the ogive the attachement hits the case mouth before you can reach 3.750"

    [​IMG]

    A more likely scenario is that they meant the overall length of the bullet from case head to bullet tip is 3.750"

    [​IMG]

    Even that is questionable because most Remington magazines have an internal dimension of 3.700", so you would not be able to stack the mag and would have to shoot single shot.
     
  7. 1CouesHunter

    1CouesHunter Active Member

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    Thanks Woods, (Also Bounty Hunter & Boomtube) This Helps Me Out. I used the Hornady OAL Gage, zeroed it out and Measured the case and Bullet just
    barely seated and could only get a measurement of 3.579"!

    I Dont think the OAL Gage will go to 3.725" with a 200 grn NAB! So, Like you said, Woods,
    **I Believe I Mistook the Overall Measurement for an Ogive Measurement.***
    I shot the Rifle with a 3.725" (tip to case Head Measurement) Shot fine out to
    600 Yards!!

    Wouldnt the Ogive measurement be around 3.100" for a bullet and case seated 3.725 tip to case head??

    Woods in that second pic, isn't the comparator sitting over the ogive of the bullet? Because when I tried to measure, the comparator was sitting on top (on the ogive of the bullet), and the lower part was exposed.

    Sorry for being slow on this...
     
  8. woods

    woods Well-Known Member

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    Yes, the comparator is sitting on the ogive. The comparator hole is actually smaller than caliber and hits the curve of the bullet down toward the tip.

    As far as the measurement you mentioned of 3.100", that would be correct if you subtract the 1.000" of the comparator body. This is the comparator reading with the OAL set at 3.750"

    [​IMG]

    I'm starting to work up loads for the 300 RUM. How far off the lands are you seating the bullet and what load are you using?
     
  9. 1CouesHunter

    1CouesHunter Active Member

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    I Just Sent my rifle Back to the gunsmith for some minor work, and when I get it back I expect I will have an exact starting point for OAL and Powder Load.

    I was using 95 grn. Retumbo, 200 grain NAB, and a OAL (casehead to tip measurement) of 3.725"

    When I get the rifle back, with the new info, I will Start at 91 grns. and work up to 95 grns.

    I also just got a Chargemaster 1500 for precise powder measurements,
    and a CED M2 Chronograph for precise speeds.