Too much shoulder bump...

TBass

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I have a 6.5 SAUM's that I am reloading for. I am shooting a 140 gr Berger bullet with 61 grains of H1000. I noticed that on half of my loaded brass I accidently bumped the shoulder back .007 too much.

Should I expect to see any real differences in velocities?
Does this have the real possiblity of dramatically effecting accuracy out to 500 yards?
 

m1match

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You probably won't see any noticeable difference in velocity or accuracy, but you will probably see shortened case life. On future loadings, I'd check the inside of the cases forward of the case head with a bent paperclip for incipient head separations.
 
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nn8734

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    I have a 6.5 SAUM's that I am reloading for. I am shooting a 140 gr Berger bullet with 61 grains of H1000. I noticed that on half of my loaded brass I accidently bumped the shoulder back .007 too much.

    Should I expect to see any real differences in velocities?
    Does this have the real possiblity of dramatically effecting accuracy out to 500 yards?
    Agree with m1match you prob won’t see any difference in meaningful difference in velocity but to confirm I’d run a small sample of rounds w/the over sized brass over your chrono to be sure and definitely keep them all separate from your other brass for that rifle.
     

    thestoicmarcusaurelius

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    I'm certainly no expert so take this with a grain of salt.

    Whether you will see a detriment to accuracy, imo, will be mostly dependent on sensitivity to seating depth of the load that you developed.

    A change in shoulder bump changes seating depth so if your shoulder bump is inconsistent then your seating depth will be inconsistent.

    Whether that inconsistency shows up on target or not depends on how sensitive your load is to seating depth changes.

    It also matters what your definition of accuracy is for this application as far as whether you are likely to notice a difference or not.
     

    TBass

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    thestoicmarcusaurelius - I track what you are saying... that being said. The O-give lenght on the properly bumped cases versus the over bumped cases is exacatly the same.
     

    thestoicmarcusaurelius

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    The way I understand it is that bumping the shoulder and extra 7 thousandths would be roughly equivalent to seating the bullets longer by 7 thousandths
     

    spife7980

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    I'm certainly no expert so take this with a grain of salt.

    Whether you will see a detriment to accuracy, imo, will be mostly dependent on sensitivity to seating depth of the load that you developed.

    A change in shoulder bump changes seating depth so if your shoulder bump is inconsistent then your seating depth will be inconsistent.

    Whether that inconsistency shows up on target or not depends on how sensitive your load is to seating depth changes.

    It also matters what your definition of accuracy is for this application as far as whether you are likely to notice a difference or not.
    No, a change is seating depth is a change in seating depth.
    Where the sizing die puts the shoulder doesn't change where the seating die puts a bullet.

    The way I understand it is that bumping the shoulder and extra 7 thousandths would be roughly equivalent to seating the bullets longer by 7 thousandths
    Yeah, relative to the case and the bullet. But that has squat to do with the chamber and no real bearing on anything.
     

    thestoicmarcusaurelius

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    No, a change is seating depth is a change in seating depth.
    Where the sizing die puts the shoulder doesn't change where the seating die puts a bullet.


    Yeah, relative to the case and the bullet. But that has squat to do with the chamber and no real bearing on anything.
    Here's what Erik Cortina has to say about this issue (starting around 6:30):

     

    BLKWLFK9

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    If it is an isolated incident and doesn't continue to be sized back .007, you shouldn't have a problem from the 1 time. If you continued to size it back .007, you are going to over work your brass and have future issues or at best case, shortened brass life. Just be sure youre bumping it .003 or less and you should be fine.
     
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    TBass

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    Spife7980 - I think I follow what you are saying and agree with you.

    Essentially the O-give to the lands will be no different between the properly bumped shoulder and the overly bumbed shoulder.

    The only thing that I might see which "m1Match" brought up is some excessive wear on my brass.
     

    thestoicmarcusaurelius

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    I think what spife may not be taking into account is that when the firing pin hits the primer, it drives the case forward until it hits the shoulder
     

    TBass

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    Bingo - I just watched the video... and that makes total sense.

    It's this type of knowledge and discussions that take place on the Hide that makes it such an invaluable tool!

    Well I will shoot the oversized cases and see if accuracy is greatly impacted.
     

    spife7980

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    I think what spife may not be taking into account is that when the firing pin hits the primer, it drives the case forward until it hits the shoulder

    Seating depth to me is measured from the bolt face. In that sense where the case is, or the empty space that might exist behind it, has no bearing on the measurement.

    What you/cortina are discussing is the excessive headspace clearance so this is where terminology places a part and Im as lacking in my vocabulary and as much to blame for when I said "has no bearing" as anyone. So yes, the distance from the lands can change by the amount of excess headspace clearance but I wouldnt call that seating depth. Id call that the distance from the lands.
     

    thestoicmarcusaurelius

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    Seating depth to me is measured from the bolt face. In that sense where the case is, or the empty space that might exist behind it, has no bearing on the measurement.

    What you/cortina are discussing is the excessive headspace clearance so this is where terminology places a part and Im as lacking in my vocabulary and as much to blame for when I said "has no bearing" as anyone. So yes, the distance from the lands can change by the amount of excess headspace clearance but I wouldnt call that seating depth. Id call that the distance from the lands.
    I agree that your terminology is better. And, it would have been better to say that shoulder bump inconsistency would result in inconsistency in distance to the lands (unless seating depth was adjusted by a corresponding amount).

    That's how I think about seating depth is setting the optimum distance to the lands with the seating die assuming consistent shoulder bump (but I can see your point that that's technically incorrect and not what "seating depth" is) and the seating die is working the same way regardless.
     
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    m1match

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    To illustrate how oversizing shortens case life, I had a batch of LC94Match cases shot in my bolt gun that normally goes more than 10 loadings before the cases start showing neck cracks or incipient head separations. I let my sizing die get out of adjustment and I was bumping the shoulders about 10 thousandths (.010 instead of .002 to .003). After 3 loadings I got a partial head separation on one case and the rest of the batch was in similarly sorry shape ready for the recycling bin.