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  1. #1
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    Shoulder Bump

    With a .224 bullet and brass with .014 neck wall thickness has anyone found .001 or .002 shoulder bump to be more conducive to accuracy using a single round fed bolt action?
    Thanks
    Last edited by firearmsunlimit; 09-20-2021 at 05:30 PM. Reason: Misstated question

  2. #2
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    way too little info to base a reply on.

    yes i have used .001 on a bolt gun
    but it was my gun my ammo and my loading process

  3. #3
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    Quote Originally Posted by rsmithsr View Post
    way too little info to base a reply on.

    yes i have used .001 on a bolt gun
    but it was my gun my ammo and my loading process
    So what would you like to know to make a judgement concerning shoulder bump?

  4. #4
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    Quote Originally Posted by firearmsunlimit View Post
    So what would you like to know to make a judgement concerning shoulder bump?
    Have you found a .001 or a .002 bump to make any difference in accuracy.

  5. #5
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    Quote Originally Posted by firearmsunlimit View Post
    Have you found a .001 or a .002 bump to make any difference in accuracy.

    No

  6. #6
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    You want the bullet as concentric as you can achieve as it strikes the
    leade and engraves into the rifling.

    Symmetry is good here.
    The closer to perfect the better.

    I neck turn cases for my varmint barrels.
    They are ALL 'tight neck chambers' and use 0.0100 inch case neck wall thickness.
    With around 0.0020 of clearance between the bullet and leade diameter.
    A factory round will NOT fit, very much on purpose.

    It makes for extremely tight groups to many hundreds of yard.
    I use my 6 mm REAM AI out to around 400+ yards with excellent results.

    Long ogive, tightly controlled leade clearance.
    Case to chamber length within about 0.0010.

    When neck hardness builds up over repeated sizing, I set them aside until I have
    around to bother tempering them.
    I then use them for fouling shots or sighting in shots a few times to get correct
    hardness back on the neck.

    That neck hardness affects the amount of force required by the powder to free the
    bullet as it begins to break down on firing.

    You can easily evaluate neck thickness variation to 0.0001" inch.
    Just use a 0.0001" dial indicator in you neck measurement tool
    instead of the more common 0.001" gauge.
    Spin the shell on a snug pilot and watch the variation.

  7. #7
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    Quote Originally Posted by firearmsunlimit View Post
    With a .224 bullet and brass with .014 neck wall thickness has anyone found .001 or .002 to be more conducive to accuracy using a single round fed bolt action?
    Thanks
    What would you gain with that tight of clearance? To put it in perspective, the thickness of a brown hair (human) is about .003".

  8. #8
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    A lot of the misconceptions concerning loaded round to neck clearance has itís origins in the Houston Warehouse Experiments.

    As a competitive Benchrest Shooter, I would say ignore all of that. You might be able to get an extreme accuracy combination to shoot some tiny groups in a totally controlled environment that simply does not translate in the real world. We do not shoot Matches in a controlled environment.

    The trend in Benchrest in the past years has been to run a little more clearance. Around .0025 loaded round clearance for 6mm and 22, .003 for the short 30ís.

    The rifle will agg just as well, and you can avoid any pressure spikes due to insufficient bullet release.

  9. #9
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    Quote Originally Posted by jackie schmidt View Post
    A lot of the misconceptions concerning loaded round to neck clearance has itís origins in the Houston Warehouse Experiments.

    As a competitive Benchrest Shooter, I would say ignore all of that. You might be able to get an extreme accuracy combination to shoot some tiny groups in a totally controlled environment that simply does not translate in the real world. We do not shoot Matches in a controlled environment.

    The trend in Benchrest in the past years has been to run a little more clearance. Around .0025 loaded round clearance for 6mm and 22, .003 for the short 30ís.

    The rifle will agg just as well, and you can avoid any pressure spikes due to insufficient bullet release.

    Actually I should have been more clear. My question relates to shoulder bump.

  10. #10
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    Quote Originally Posted by firearmsunlimit View Post
    Actually I should have been more clear. My question relates to shoulder bump.
    .001 to .002 should be just right.

    As you fire the cases more, you might have adjust your die a tad down to maintain this as the brass tends to work harden in that abused area and refuses to give as much.

    For my competition rifles, (30BR, 6PPC), I actually lean more toward .003 to .004 for ease of loading and extraction.
    Last edited by jackie schmidt; 09-20-2021 at 08:12 PM.

  11. #11
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    Back to your original post. Shoulder bump will not affect accuracy.

  12. #12
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    Quote Originally Posted by jackie schmidt View Post
    .001 to .002 should be just right.

    As you fire the cases more, you might have adjust your die a tad down to maintain this as the brass tends to work harden in that abused area and refuses to give as much.

    For my competition rifles, (30BR, 6PPC), I actually lean more toward .003 to .004 for ease of loading and extraction.

    "adjust your die a tad down to maintain" How? remove material from shell holder or maybe the bottom of the die? I have three different presses, none of which have any means of positive stop that would allow for a repeatable stroke (short of contact between shell holder and die)?

  13. #13
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    Correction

    Quote Originally Posted by firearmsunlimit View Post
    with a .224 bullet and brass with .014 neck wall thickness has anyone found .001 or .002 to be more conducive to accuracy using a single round fed bolt action?
    Thanks
    what i was trying to say relates to shoulder bump.

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