School Me on Measuring Finished Cartridges

Discussion in 'Handloading and Reloading' started by sisyphus, Nov 30, 2021.

  1. sisyphus

    sisyphus Member

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    I never ran into this until I started loading 308. I guess my pistol calibers and 223 weren't subject to big enough variations that it alarmed me.

    Last time I loaded 308 I was having to adjust my seating die every 2 or 3 cartridges. So after that session I ordered a micrometer seating plug for my die.

    Today I sat down to load with said plug for the first time. I also used same headstamp once fired brass that had been trimmed and sized.

    Even with the micrometer seating plug, I was getting variations of OAL of around 10 thousandths of an inch, with the OAL I was shooting for dead center of that 10 thousandths range. It was a real headscratcher, but since my finished cartridges all were well within saami spec for oal, I finished the tray I was making, then went downstairs to Google why.

    So I gather after Googling this that even same headstamp brass is going to give this issue when loading rifle cartridges. Funny that my 223 seems to all measure out the way I'd been doing it. Anyway, what I took from the forum posts I read about it is that I am just going to make myself crazy measuring base to tip like I have been.

    So I will order myself a Hornady comparator and anvil with a 308 insert to clip on my dial calipers. Would someone give me a quick rundown of how to properly measure this way? I am guessing I take one of my finished cartridges that is perfect in every dimension, throw it in the comparator, and then make all my 308 to that measurement. I gather this will give me cartridges that will still vary in tip to base oal, but will be within a couple thousandths from base to ogive. That sounds to me like I'd be making more consistent ammo.

    Still a novice guys, don't feel like you're talking down to me. I want to make the best quality ammo I can using the tools I have. Thanks!
     
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  2. MikeInOr

    MikeInOr Member

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    What bullets are you loading? Slight differences in the ogive can translate to large differences in OAL.

    I have never worried about "perfect" ammo. I strive for accurate ammo with repeatable results. I.e. before I make any big changes to a load or the prep for the load or purchase any expensive gear I take the load out and shoot it. The proof is in the pudding... if it shoots well and keeps a tight group appropriate for the rifle I am happy and run with it. If it doesn't shoot well I will run it through the chronograph to see how repeatable the speed of the bullets are as a starting point to look for improvement. In my experience finding the right load for the rifle is much more important than minor differences in OAL.

    Work up the load for the rifle first. After you have a acurate repeatable load for the rifle you can start chasing the ever dimishing returns of loading "perfect" ammo.
     
    Last edited: Nov 30, 2021
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  3. sisyphus

    sisyphus Member

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    Hornady 150gr FMJ
    it's cheap and I shoot a lot
     
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  4. JimKirk

    JimKirk Member

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    First ....many times a magazine determines cartridge length ...

    The Hornady is fairly easy to use ...biggest problem is making sure you have the cartridge face flat ... get several readings off the same piece ... when you get the same reading ...it will become evident that you are doing it right ....got kinda get the "feel" ....

    Ogives do vary especially in different lots of bullets ....

    If you want to get more precise .... measure the actual bullets them self ... group them by lengths ....

    Then try seating some of the the same lengths into cartridges ....then you can figure out what is going on with your seating process ....
     
  5. Chuck R.

    Chuck R. Member

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    Do yourself a favor, before you go insane...

    Measure some bullets 1st using both the comparator and just the calipers, not loaded rounds. This will give you an idea of the manufacturers tolerances that you're dealing with.

    After that, chances are you'll feel pretty good about your loaded ammo.

    I use both methods to measure...just in case. A comparator is only good at measurements that are taken with it, no two I've seen are exactly the same. Hence the old base to tip measurements I take. I take measurements in 10rd samples and record them in a spreadsheet. When I measure a cartridge using one method I flip it upside down, as to ensure I measure the exact same cartridge using the other method. The spreadsheet provides me the average and SD for the sampling for both measurement methods.

    Usually the comparator method is more consistent, but with both methods you will see a variance in the manufacturers tolerances.
     
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  6. MikeInOr

    MikeInOr Member

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    Hornady 150gr FMJ are perfectly acceptable bullets but they aren't match grade bullets. I would bet there is some variance in the ogives that accounts for the OAL variances. If you want to load match grade ammo start with match grade components that you have weighed and sorted.

    You are chasing a very minor difference in your ammo that will results in very minor accuracy and repatability variances. There are many other much more signifigant factors that you need to address before you start obsessing about minor differences in over all length.
     
  7. sisyphus

    sisyphus Member

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    I just measured 10 out of that box of bullets, and they ranged from 1.117 to 1.132

    lol

    should I just keep making 308 the way I have been? If my finished cartridges have a 10 thousandths range in oal measured base to tip, and my ideal oal is dead center that 10 thousandths, is it good enough for government work?
     
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  8. sisyphus

    sisyphus Member

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    I'm just shooting steel out to 800 yds. Am I expecting too fine a result at the bench? If the variations I have encountered are normal, I'm ok with that. The ammo I've produced has functioned just fine, and the rare occasion I've shot paper I've had some one moa groups with it, which I thought was all I could hope for using inexpensive FMJ.
     
  9. MikeInOr

    MikeInOr Member

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    Yes, that variance in OAL is perfectly acceptable for the bullets you are using.
     
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  10. MikeInOr

    MikeInOr Member

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    Yep, you are going down a rabbit hole that I and every reloader I know have gone down when starting to load for accuracy. If the ammo works as is then use it.
     
  11. sisyphus

    sisyphus Member

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    so what is an acceptable deviation in oal when I am loading 308? What would you live with that wouldn't make you think you had a problem in either hardware or process?
    Thanks guys.
     
  12. mshootnit

    mshootnit Member

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    You use the hornady OAL comparator to give real, accurate measurements for your reloaded rounds because the Ogive should not vary at all from bullet to bullet. Mine are usually uniform down to one or two thousandths of an inch. If your equipment is working properly you should be able to achieve this level of uniformity.
     
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  13. mshootnit

    mshootnit Member

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    If I were getting 10 thousandths variance from one round to the next, I would troubleshoot some things. Does your press cam all the way over when you are bullet seating or come to a dead stop at the bottom of the stroke? If it comes to a dead stop, are you pressing down with the same force each time? Are your dies clean, adjusted according to the instructions according to whether or not you want a crimp, screwed all the way in? Are your primers all seated at least flush with the base of the case, and uniform? Make sure your die is pushing down on the bullet ogive when seating and not touching the nose of the bullet. Clean and proper shell holder?
     
  14. mshootnit

    mshootnit Member

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    What I would do is just stick to the comparator measurement for all purposes, and not use the OAL base-to-tip, except just to make sure it fits easily in the mag. The Ogive measurement should be uniform, and that is all that matters. The bullet tip matters relatively little to practical accuracy.
     
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  15. MEHavey

    MEHavey Member

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    I assume that's tip2tail bullet OAL.
    You'll find the ogive/comparator dimension variance will be only a coupla thou....
     
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  16. IALoder

    IALoder Member

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    I've loaded a ton of these in .308. .010-.015 variance in COAL with the same seating die setting has been normal with em. I set it to where my desired COAL is in the middle of the range, and get after it. If you're close to mag length you'll have to be careful though.
     
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  17. cfullgraf

    cfullgraf Member

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    There are a number of factors that affect cartridge overall length when seating bullets. For instance, if you are looking for a particular seating depth and make several adjustments to reach the desired COL, then when you seat a next bullet to the "final" seating depth, the COL will be different.

    Just how you operate your press will induce some variability in the seating depth. Different speed in seating the bullet will induce some difference in COL.

    Cheap, ah, inexpensive, bullets will have greater variability in COL. The reason they are cheap is the manufacturer does not take the care of the bullet dies as they might with match rated bullets. Bullet manufacturing companies make bullets in many different production lines that have different forming dies. So, from bullet to bullet, dimensions will change a little. Albeit, the differences are small, but they are they are there just the same.

    Anyway, for blasting ammunition that you are loading to fit a magazine, make sure the maximum COL fits the magazine and let the short length fit where it may.

    Try to operate the press as consistently from bullet to bullet as you can.
     
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  18. dcloco

    dcloco Member

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    EXACT info.

    There are differences, even in "match" or other bullet varieties.

    Agree with MikeInOr.......!!!!
     
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  19. Bcwitt

    Bcwitt Member

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    I dont consider a variance .010 to be a concern. As was said, likely have that much difference from one bullet to the next.
     
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  20. Walkalong

    Walkalong Moderator Staff Member

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    Yep, you're doing just fine with your bullet of choice, if you want to improve accuracy/consistency/groups down range, you'll need to step up to a better bullet, but since it is working for you, and under 1 MOA is just fine with it, do you want to spend more?
     
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  21. South Prairie Jim

    South Prairie Jim Member

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    I never measure the (overall length) after determining my Base to my ogive settings for my seating die. Inconsistent Bullet hold/ Neck tension or the lack of can have a huge effort on seating depth variations.
     
    Last edited: Dec 3, 2021
  22. GeoDudeFlorida

    GeoDudeFlorida Member

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    Well, having come late to this party, all I can add is, it matters more where you measure than what you're measuring. When I was first starting out in aerospace I worked the burr bench - sanding and filing station for in-process and complete materials to remove burrs and finish imperfections. New deburring-bench operators - yes, that is the term - tend to remove material that don't need removing and the inspectors are all over that area keeping on eye and how tools are held and operated. A flat-smooth hand file can scrap a $10K piece of titanium in a single stroke. What I learned real quick was, measure the surfaces that matter, not the surfaces that don't matter. Measuring the very edge of a bar will reveal where you've rounded and undersized while 10 thousandths off the edge measures fine. It depends on where your micrometer seats. That's why using a comparator to grab the ogive makes a difference. Also check your bases. A slight jacket overrun on partial edge makes zero difference in actual performance down the barrel but will add or subtract 1-2 thousandths when you put a mic to your comparator/bullet. Ten you're wondering why your bullets are "bent" or "slanted."

    Stay sane and remember, it's just target shooting, not rocket surgery. ;)
     
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  23. SSN Vet

    SSN Vet Member

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    Disassembly your die and see what the plug looks like. More often then not they contact the bullet on the ogive and thus any variation in bullet geometry can affect COAL.

    I used to drive myself nuts chasing thousandths of an inch for COAL, but the most consistent I can ever seem to achieve is +/- 0.002".

    =/-0.010" does seem like a lot, however, but if the bullets vary in shape, it may be the best you can achieve.
     
  24. Thomasss

    Thomasss Member

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    Comparators are nice and I use it every time I load a different bullet because of the difference in the ogive. But I also have a Garand and a 1970 Rem 700 also in 30.06. It's very hard to match run out when the gun barrels have throat erosion. I been told to try dropping a 1/4" dowel down the barrel when using the comparator to help find the correct seating depth. Also remember it's hard to get all brass trimmed exactly the same and that will also give you some variance of your over-all length (OAL). I try very hard to match the OAL but find I am usually off a little. I shoot sub-MOA .75 with the Remington and have a doe in the freezer, so I'm happy with that. If you are not sure of the exact seating depth, you may want to try some slightly different seating depths and judge the best one yourself. "Aim small, miss small."
     
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