seating depth problem

Discussion in 'Reloading' started by cookjp, Apr 11, 2011.

  1. cookjp

    cookjp Well-Known Member

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    Ok Guys help this newbie out. I am having trouble getting consistent seating depths for my 22-250. I set the seating die up and load a few and get the same reading then I will have one or two that are off by up to a hundreth or so then they will go back to the set up lenth. I am using a Forster benchrest seating die and loading brass that is all cut to the same lenth. Loading 53gr hornady match hollow points I have measured the bearing surface on all and they match. The brass is mixed head stamp but all preped to be the same. help I am lost on this one.
     
  2. CRNA

    CRNA Well-Known Member

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    Ok, I'm new at this too, so it may be a case of the blind leading the blind here. I ran into the same problem. Then I measured the lengths (overall length) of several of my SMKs and they varied by a thousandth or so. I think its just a difference in the meplat in my case. Possibly the same problem you are having. I just get them close to the OAL I want the loaded cartridge and go with it. If you keep changing the seating depth then you are going to be chasing your tail I think. If you do it that way then you are going to end up with a different OAL every time you change. I just make them all the same and don't try to chase it down.
     

  3. BuckSnort

    BuckSnort Well-Known Member

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    Two questions..

    How are you measuring OAL?

    Is it a compressed load?
     
  4. flashhole

    flashhole Well-Known Member

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    That's my question too. How do you measure OAL? If you are measuring from the tip of the bullet and not a point on the ogive you will never get consistency and lengths will be all over the map.
     
  5. CRNA

    CRNA Well-Known Member

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    Don't mean to hijack, but how do you do that? How do you measure from one particular point on an ogive and get consistent readings?
     
  6. RT2506

    RT2506 Well-Known Member

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    You need to measure from the O-give of the bullet to the base of the case. You need a bullet comparator to do this. There a different types of comparators. Check them out at Midway PTG comparator product # 365-447 & 746-974 or Hornady product # 348-740 .

    Bullet tips are different but the O-give is usually consistent in the same lot of bullets. Where you can run into problems is if the bullets came from different lots or were made on different machines.
     
  7. cookjp

    cookjp Well-Known Member

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    I am using the hornady comporator set to measure OAL off the bullet ogive, and it is not a compressed load.
     
  8. BuckSnort

    BuckSnort Well-Known Member

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    Ok.. Is it possible that some of the primers are not seated to the bottom?
     
  9. cookjp

    cookjp Well-Known Member

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    I believe youre right Buck Snort, I got to thinking the same thing and checked a few and sure enough not all the primers were seated flush. I have had these shells awhile and was trying to use them up and guess these were preped before I started uniforming primer pockets. Thanks for all the help guys.
     
  10. gunner69

    gunner69 Well-Known Member

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    Here is a solution to accurate seating depths consistently

    [ame=http://www.youtube.com/watch?v=etgIVSSl8L8]CONSISTENT BULLET DEPTH SEATING - YouTube[/ame]
     
  11. Mikecr

    Mikecr Well-Known Member

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    The video illustrates a real problem for seating and other bullet measurements(like bearing comparisons), which is ogive radius variance. You can address this by qualifying ogive radius on your bullets right up front, like he was doing, or with a Bob Green bullet comparator(made just for this).

    Missing from the video was realities associated with nose datum affects to consistent measurements. We all want land contact point consistent, but this is not always the best datum for good measurements, as it is also not a best contact for seater stems.

    The stem that caused 14thou of contact difference was poorly suited for those bullets, as this is beyond affects of ogive radius variance -that low on the noses. But still, it's refreshing to see someone investigate the problem like he did.
    Smaller differences are common in-lot, larger lot to lot.

    Be careful not to refer to an 'ogive' as though it is the land contact point(that's not what ogive means). To date there is no such point established as a standard, and it will always vary locally.
     
  12. boomtube

    boomtube Well-Known Member

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    CRNA: "How do you measure from one particular point on an ogive and get consistent readings? "

    The various comparitors all have a bore size hole (or near) in them; groove size bullets enter and stop at the correct point on the ogive. Readings are taken from that ogive contact point to the head of the case. (A compensation/correction is made for the body length of the comparitor itself.)













    NS
     
  13. gunner69

    gunner69 Well-Known Member

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    The stem did not cause the 14thou difference. I selected that bullet to show the extreme example. The curvature of the bullet caused the 14thou difference. I can prove this bc I will get the same reading on a particular bullet 10 out of 10 times. The method shows the inconsistencies in the curvature of the bullets and NOT in the seating stem. The point is that when you buy a box of bergers most of them have a 1-3 thou tolerance in the curvature/ogive but then there are those few bullets that are way way out of tolerance that will seat drastically different than the rest. These bullets are your fliers and should be culled from the rest or collected to be seated and used as a group. when i have the chance i will prove this by doing a video at the range comparing groups of bullets that are consistently seated vs those that are way out of tolerance mixed in and seated using the same die setting as the rest of the batch. you will be shocked.
     
  14. Mikecr

    Mikecr Well-Known Member

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    Ok gunner. My contention is that in-lot ogives usually don't vary so much as the 14thou anomaly, and I agree this would be a flier.
    I've also found that gizzies like your reamer cut insert work alright with secant ogives, but less so on tangents. In the case of tangents, your original insert would probably produce better results(depending on the leade angle and ogive radius).

    For qualifying ogives, it's best to set mid point-ish datums for comparison, so that you are away from extremes(meplat & leade contact).