Hornady LNL OAL gauge question

Discussion in 'Reloading' started by CRNA, Jul 5, 2011.

  1. CRNA

    CRNA Well-Known Member

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    I will try to make this as brief as possible. I ordered a Hornady LNL OAL gauge to help me more precisely measure my handloads. I may be doing something wrong, (as I am known to do from time to time), but I need a little help here. First off I measure my OAL (from the ogive) with this tool using my SMK 168gr bullets that I have been using for my rifle. I get a little variation in my measurements, but I feel like it's probably just me getting used to the tool and putting varying amounts of pressure on the ram driving the bullet to different depths into the lands/touching the lands etc. So I make about 8 measurements until I can can get a good idea as to where the lands are. For example, I may have some measure a few thou one way or the other, but I see the same repeating number on the calipers for several measurements and determine that is my OAL. Now I try some Berger 168gr VLDs that I just ordered. (They were on sale at Midway and I thought I would give a box a try.) The thing is, I would expect that since I am measuring from the ogive (with a bullet comparator) the OAL would be the same. Makes sense to me. But I am getting a different OAL value from the SMKs. After measuring multiple times, I have determined that the OAL of the SMKs is 2.720". The Bergers however measure 2.750". It seems like a HUGE error to me. Maybe I'm doing something wrong? Or maybe I just can't wrap my mind around why they would be different? Any insight here would be greatly appreciated.
    Steve
     
    Last edited: Jul 5, 2011
  2. Mikecr

    Mikecr Well-Known Member

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    The context of ogive is often assumed as the point where lands would first contact a bullet nose. That's the datum desired.
    But a bullet ogive is not a datum point. 'Ogive' is really a term to define the curve of a bullet nose, rather than a specific place on that curve.

    That desired datum(first contact) varies with angles, both related to the nose curve, and the bore leade angle. And while a datum can be calculated, your tool will not match it.
    The only matching tool that I know of is a barrel stub throated with the same reamer used to cut your chamber('gizzy').
    Without this, you still have a relative datum provided by your tool. It is simulating land contact.

    But no matter the tool, the datum provided will change with each different nose curve, cuz different nose curves actually do contact lands differently.
    Same lands(simulated or not), but tangent ogive curves(SMK) are way different than secant ogive curves(VLD), so the datum moves.

    All that matters is that you determine ogvOAL for EACH bullet type you intend to use & log it.
    Focus on reproducing these lengths based your measurements, with your tool.
    Hell, I use is a Sinclair 'nut' (nothing fancy). But as long as I can reproduce the exact seated measure with that tool, I'm good to go.
     

  3. MSLRHunter

    MSLRHunter Well-Known Member

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    Mikecr speaks the truth. You must measure every type of bullet you shoot because they will all be different.
     
  4. CRNA

    CRNA Well-Known Member

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    So in short, I am measuring correctly and the measurements for the two bullets will be different?
     
  5. 338winmag

    338winmag Well-Known Member

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    CRNA - Yes, different bullets will have different measurements.
    Just a thought: Usually bullets from the same lot\box have little variation so no real consideration needed... Double check on new lot\box in case considerations are needed.

    Mikecr. Excellent explanation.
    Sometimes I agree with you.. sometimes maybe not so much... but you have some great head knowledge and this explanation was super and greatly appreciated.

    For all my rifles I most often get a deviation of .0005. An occasional deviation of +- .001 happens but rarely now that I am very familiar with my Hornady gauge and how to use it on each rifle. Bottom line as Mikecr states... one can use most anything to acquire a base measurement as long as it is consistent.

    "... Focus on reproducing these lengths based your measurements, with your tool."

    Thanks Mikecr and good topic CRNA
     
    Last edited: Jul 6, 2011
  6. CRNA

    CRNA Well-Known Member

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    Thanks guys. I saw variation between the SMKs and Bergers, but I didn't see any variation between the individual boxes of bullets.
     
  7. joe0121

    joe0121 Well-Known Member

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    Also I noticed that I really had to make darn sure I had the modified case perfectly strait to get consistent readings. Still waiting on my Micrometer adjuster for my seating die to come from Hornady. Turn 1/8 turn, measure, repeat. Is a pretty tedious process every time I wan to change the Amount of jump I have.
     
  8. newmexkid

    newmexkid Well-Known Member

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    Same thing happened too me until an old gunsmith told me I had to measure every different make bullet.
     
  9. sp6x6

    sp6x6 Well-Known Member

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    CRNA, Here is a little more info on your measuring with Hornady gauge. If the gauge is ''THEIR'' supplied brass it is typically short, most of mine where .005 short in several different calibers compared to fire formed brass in said rifle. If you send them your fired brass for gauge then OK. You can also determine this with a gauge measuring shoulder on thier gauge versus your fired brass, then take the difference into account
     
  10. CRNA

    CRNA Well-Known Member

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    You make a good point. I measured my brass vs. their brass with my headspace gauge. I can't remember the discrepancy, but I do know that it was significant. I plan on taking the difference and adding that to the equation to get a more exact reading. Thanks for bringing this point up though. Someone reading this post and not realizing could have been making ammo not quite as exact as they thought.
     
  11. fj40mojo

    fj40mojo Well-Known Member

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    For what one of Hornady's "Modified Cases" costs you can purchase the correct tap 5/16-36) and tap drill (7mm) and modify your own fire formed brass. Zero disrepency.:)
     
  12. CRNA

    CRNA Well-Known Member

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    I plan on doing that for some of the other calibers that I load for. I just happen to be working on some brass right now and my brain is dead. My LNL gauge says that my OAL to load to the lands for a SMK is 2.750". My fireformed brass is .015" longer at the shoulder (using a headspace gauge). So to seat a bullet in MY brass to touch the lands, would I not SUBTRACT .015" and load MY brass for MY gun to an OAL (measured at ogive) to a measurement of 2.735"?


    Oh crap. Now I'm thinking too hard and that doesn't make sense. Both cases are the same case trimmed length, so what would it matter. Now I'm thinking that they would be loaded the same. My shoulder has just progressed forward to fit my chamber, but the shell trim lengths for both my brass and the "modified case" by Hornady are the exact same.

    Help somebody.
     
  13. joe0121

    joe0121 Well-Known Member

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    I trim my brass a bit short just so I can get it the same length. Then sort it by brand and weight. I might start turning my brass and setting my lee neck sizer for a tiny bit of crimp to get some more neck tension. Though I'm not sure I see the point. i think if I get 1/2 MOA with my current process I'll stop. The least amount of steps the less chance for a screw up. Anyways 1/2 MOA bipod unsupported is about as much talent as I have anyways I really need to get in shape breathing is my main killer that and I get the shakes a little bit.
     
    Last edited: Jul 10, 2011
  14. joe0121

    joe0121 Well-Known Member

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    Do you have the bushing set so you can measure or the ogive instead of the tip? The shoulder should not affect your measurements. you are measuring from the base of the case to where the bullet touches the lands. This should be doable regardless of the shoulder.

    The distance from the base of the case to the throat should never change(except for throat erosion obviously) just like the distance from the face of the bolt to the chamber should never change as it is fixed. Or should be Since your seater die does not touch the shoulder is will seat the bullet to a length in relationship to the base as it sits in the shell holder. As such when you chamber the round the base of the case sits on the bolt face and the bullet should be the same constant distance from the bolt face regardless of the shoulder. The only thing that changes is the head space. I did a little experiment I took a fire formed case and a brand new case that has only been annealed. I ran a Hornady 208GR Amax That I pre weighed to within .1 gr and measure to be within .006 in lenght. Seated a bullet in both and came up with a OAL that was exactly the same using my LNL bushings. The heads peace was .005 off as this is on a brand new barrel with 25 rounds down the tube.That error was likely me not having the case perfectly strait in my calipers.

    Now taking your original measurement is a different story if you have a very loose chamber and the modified case goes in further that your once fire brass that has been fire formed. This would obviously affect the position of the base of the case as it is not being controlled by your bolt. FYI Hornady will modify your case for you, which they recommend VS using one of their modified cases.